The developers have previously tried to explain the peculiar relationship between the two games:
https://www.gog.com/forum/general/the_marble_nest_by_icepick_lodge_new_download_link_for_everyone/post9.

Why did the demo get removed?

Allow me to explain: Pathologic is the original game released in 2005 by Ice-Pick Lodge. It was the first game they made and was highly ambitious but also unpolished, with a notoriously opaque English translation. After producing several other games, the developer launched a kickstarter in 2014 to remake the first game, with the goal of more fully realising their original vision now that they had more funding, experience and time. This included experience remaking their own games, as they did with The Void. The new version of Pathologic they were planning came to be known as the Pathologic Remake to most.

Both during the kickstarter and afterwards, the question arose whether this would be a faithful remake or whether the game would veer off into different directions, as due to the poor translation there were many people who had never played through the original and who were hoping to see a faithful remake, while others wanted something new and different. In order to satisfy both, Pathologic Classic HD was released in 2015 with fixes and a new English translation, so that a playable version of the original would always exist. This way the new version was free to do its own thing.

Later, in 2017, Ice-Pick Lodge partnered with tinyBuild as their publisher and the game was officially renamed Pathologic 2. It was announced that the renaming was done in order to avoid confusion, as there were now quite a few things associated with that name (Pathologic, Pathologic Classic HD, Marble Nest, and so on). Eventually, as development took longer than planned, they announced to release the game in parts after having had to break promises regarding when it would release multiple times. Haruspex was chosen as the first campaign to release due to this. This is also why the other two campaigns are likely further along than you might think, as the goal had been to release all three together.

History aside, think of it as them revisiting an idea that is dear to them and which they weren't able to fully explore last time. Ice-Pick Lodge is not a studio that makes these decisions with financial gain in mind, as all their games have been weird, hard, niche titles made without compromise.

^ Serious question given the above comments - if the game was just released with only one of three playable characters and the other two are planned to be added later on as perhaps "Pathologic 2 Campaign DLC", then given that the publisher is TinyBuild, exactly how guaranteed is it that the GOG version of Pathologic 2 will actually be completed here instead of ending up like Party Hard 1-2 regarding "missing" post-launch DLC and a shrug from TinyBuild whenever someone emails them about it?

I didn't get a chance to download add the demo to my account and now it seems to be gone. Weird.

I downloaded the demo (11GB) yesterday just to see that key rebinding is NOT working in the demo at all. While the menu exists it is impossible to rebind any key. Seems to be the same in the Steam release of the demo. Hopefully this is the reason why the demo has been removed - to fix this. Offering a demo while omitting crucial basic features some people need to even enjo the game is imo more than a bad decision (if it was intended that is).
I would rather like to ask GOG why they even ALLOW publishers that leave games unfinished and unupdated here to release another game here AT ALL. You want to release another game on GOG? Bring your old game(s) up to date and we can talk again. Where is GOG's curation in such cases?

There is a setting "invert mouse" but it also does not seem to work in the demo so I cannot test it. Strangely enough I can look up/down with my controller by pressing left stick left/right ... this demo really seems to be broken.

For the same reasons for which there are (and continue to appear) games in the GOG catalog that have not the fact that there is no support, but even their creators no longer exist as such.
We get the game in the form in which it is at the time of purchase. And nothing else. And GOG is nothing different from others, such as Steam/EGS/you-name-it. Even in Steam your "guarantees" ends 2 hours later after the purchase/play. And if you are unhappy - you can refund. Nothing more.
And no one promises any further support and does not guarantee. Again, neither here nor in Steam.
Given all this, all these cries are incomprehensible, about the ban on the sale of games, the developers of which do not support the game after release. I myself am very unhappy with such cases, but you either buy the game as it is, or the state of the game does not satisfy you and then you do not buy it.
If the state of the game does not suits you, but you still buy, in the hope of some future patches there - then this means you are doing something wrong. And encourage the similar approach of the creators of games.
No need to take my text hostile. It’s just obvious that GOG is full of selling games without support, and this case is in fact nothing different. Therefore, the choice is always the same: if the game suits you, you buy; if not, you do not buy.
If it seems that the game will be better in the future (for example, after the release of patches), wait for the release of patches and buy the game when it becomes the way it suits you.

Thank you for spelling out the pure legal situation which I was fully aware of by the way. However this is NOT about the legal situation it is about the fact how those publishers treat GOG different than Steam (which will ALWAYS be updated - no matter if they are obliged to do so or not) and this is about GOG who with such steps does not prevent publishers/devs treating them and their customers worse than Steam customers. You might not know it but many already left GOG because they said that DRM-free is not as important as a game that's up to date. GOG is actually KNOWN to have several games that are not updated. If you really think just because people don't have any legal obligations to those updates that they should stop complain something really went wrong. Again: I would not complain if this would happen on Steam the same - but that's simply not the case.

We are also not talking about 1 or 2 games as you can see here (not all games on the list are about missing updates but far too many).

I am really not sure what to think about this release. I love their previous games. I played original Pathologic with all three characters, it took me around 100 hours to finish it (I usually take my time with games, but it's also true, that doing everything in that game indeed takes a long while). While the game had some technical and quality (low-budget) issues, it remains unbeatable as a unique experience, an art masterpiece.
I would love to see what they have made here, but... On screens the game looks almost the same as original one. Characters, locations and gameplay seems basically the same. From reviews I can see that animations are still low quality. It really makes me ask: What the heck have they been doing for these last few years?
Maybe if it was a full package, but it's only 1/3 of the campaign. And there's no explanation how much the whole game will cost. I guess I will wait for more reviews and also see how the situation is going to evolve. I like to buy "complete" games, so unfortunately I must wait. Sorry, Ice-Pick Lodge. I really, really hope you can make it right and I still think that you are making most intriguing and unique games

This is not just LEGAL situation. It's just fact situation.

This is not true. Steam is full of games, the developers of which have abandoned updates. Just the period during which updates are carried out in Steam, most often longer. Because a game in Steam brings income longer. Whining on the forum will not change it.

I repeat: GOG is FULL of games, which will never get updates from developers. Fallout 2 for example. Or Vampire: The Masquerade - Bloodlines. "Banning" "games without support" will not help in any way. Just now we have 500 games with support, and 1500 without support. And there will be 500 games with support... And nothing more ...
You have a rather stupid and short-sighted idea. Just do not buy these 1500 "games without support".

Yes, but your proposal does not fix this situation.

But if GOG does as you suggest, GOG will be KNOWN as a store with just a few games. At all.

I don't just think. I KNOW people don't have any obligations to those updates. And you know. You just WANT for it to be different. But you KNOW that in reality it is. And the most important thing that really went wrong here: that you do nothing to change it. And just whine on the forum. The developers here do not even read you. If you really wanted to convey this thought to them, you would write to developer's support.
But you just want to be loudly worried about it here.

This happen on Steam. Sooner or later EVERY game on Steam stops getting updates.

This link is useless in the context of a conversation. Just look into it and do not buy the game if the game does not suit you in the form in which it is. This is the ONLY winning strategy.

I'm not pleased that the game currently has 1 out of the 3 characters, but IPL explained their financial reasoning on the Kickstarter, and I believe they are passionate and serious about the game enough to at least want to see it to conclusion. The publisher's track record on GOG is poor. The distinction between Pathologic, Pathologic HD, and Pathologic 2 is veyr muddy at best. If you take issue with these, it's absolutely fair for you to not purchase the game. I backed the Kickstarter in 2014 and I had no way of foreseeing this, so I would take pause too. I thought I was backing Pathologic HD!

No, you saying "why they even ALLOW publishers that leave games unfinished and unupdated here to release another game here AT ALL."

Show me where we can see "product life time" for this game: https://store.steampowered.com/app/22370/Fallout_3_Game_of_the_Year_Edition/
Or this: https://store.steampowered.com/app/38410/Fallout_2_A_Post_Nuclear_Role_Playing_Game/
Developers/Publishers decide what is the products life cycle of the game. For every store separately. Often, even they do not decide, and decide the circumstances. For example, in the event of a developer bankruptcy.

No, you talking about banning games from GOG in some cases. That's from our discussion started. Try to concentrate. Not on the description of how you see the ideal world, but on your own suggestion. Tell what this will lead to in practice, for example.

Do you have any problems with the perception of what is written? Or with reading? I mean exactly what I mean.

You talking about banning games from GOG in some cases. And how do you determine whether the game has already reached this stage or not?

I don't call you stupid. I don't have such information about you. I call your idea stupid. And in this I have no mistake.

Just imagine, someone from GOG do as you want. Describe what will happen next.

That is true. This would definitely minimize the number of games here.

Well, of course. Of course it will be so. The idea is simply not to engage in the release of games here they certainly will not come to their heads and get "the same money" on Steam.

Of course not. Just from the list of games will disappear games that are not being updated here by their developers. And there will be no new games of these publishers. Simply put - there will be even less games. Who will benefit from this? Whiner like you?

They are already here. Nothing will change in this part.

And what will it give? Will you sit and be happy, and the rest will not be able to buy a game that could appear here, but will not appear because of your great idea of a perfect world?
Great plan. I have a business proposal for you: write in support so that they do exactly as you ask, but only with Linux games here. I will support you in this.
Such brilliant ideas - you need to start somewhere.

You can complain right now - you can not buy games from such developers/publishers.
Here's what you haven’t explained yet: why do you want others to be unable to buy this games?
You are now like those guys that are unhappy with the appearance of some games here and require them to be removed.

Yes, I noticed that you are trying to organize a ban on the publication of some games here in order to amuse your ambition. You are not going to just do what you propose. You want the impossibility of buying such games for you (and everyone else at the same time) organized by the administration of GOG. In compulsion.
Remind me: did you ask other users of GOG if they want to live in such your "perfect" world?

The link is completely useless. You just shifted the conversation to discuss just that. And the conversation is actually about your proposal to the administration.

This game was released 5 years ago. If I know about this problem at the time of purchase, I just will not buy the game here. And I advise you the same thing (and already advised in the previous post).
But now I have a question:
And if in Steam the fix did not come out, would you be happy and everything is OK and the publisher could release new games here?

Your problem is purely psychological and has no relation to updates in reality. As we found out, the point is not that there are no updates to the games (you are quite ready for this situation). The problem is that sometimes you find out that the update is absent only here, but it is in Steam.
I think the best solution would be not to ban such developers from GOG, but to ban you from Steam. So that you do not get so annoying information. And everything will be fine.

Ice Pick Lodge has always been reliable in their GOG support. Their games are up to date and all the games that they were able to release here, they did. A drm-free version was also part of their kickstarter promises and so they would be screwing over part of their backers, which would be a strange thing to do considering how niche this games is and how important positive word of mouth has been to its relative success. There's nothing to gain from not supporting the GOG version.

However, as with any game that is unfinished, there are never any guarantees that the game will indeed be completed as promised. Ice Pick Lodge could suddenly go under, they could go back on their word, they could be unable to finish the campaigns, etc. Therefore, if you're considering buying the game, buy it for what it is and assume that nothing else will ever come out. Each campaign fully stands on its own, so you won't be left with an unfinished story, even if questions about the overall mystery remain.

yeah, that's something I'm not sure is expressed enough. one character = one complete story told from their perspective. Pathologic was essentially three different games in one, with common setting and characters and plot, but the personal details are all wildly different. people more informed than I have beaten the game as the one playable character. however, there's a deep deeeeeep rabbit hole of meta plot and lore and character insight that only makes sense once the other two playthroughs are finished. I'm not exactly over the moon about it, but it is what it is. is it unfinished? yes, in my opinion. is the game completable as is? sources say yes.