I've tried to put Hybrid Wars into my cart (I already own a couple of Wargaming games), but I don't have any discount. Checked up to the checkout page, and still nothing.

This might be it - or (after reading the post above) you need to own Hybrid Wars to get the discount for it.
This would be so much easier with a little bit of communication from GOG ... GOG/Communication ... the old problem.

The multi-player part must be the real part of the game or I cannot see why.

You need to own hybrid wars to get a discount on hybrid wars? I am lost!

At least a couple of achievements (and the game also has in-game achievements) have been bugged for a long time, and the developers never bothered to fix them. I guess that will never happen then.

Never played a second of multi player and still enjoyed it.
That's likely - then again some of those achievements are multi player only so with that possibility gone you won't get 100% achievements anyway.

Oh well too little too late.

Definitely need to use Galaxy, in order to play as Ivan, even in singleplayer. The game says "Available after login to multiplayer." for him, if I load the game without Galaxy.

Yes and no. IIRC you need to login once through Galaxy to be able to create an account on wargames.net. After doing this you will get a ticket downloaded on your PC and after it has done so the Ivan Character will stay active even if you don't use Galaxy to start the game. I've tried like crazy to fiure out what the registration has changed in my system (noticed some files in the game folder but removing them did not lock thecharacter again) but without any success. So tbh I don't know what exactly happened locally the moment I created that account but I tried to access the Ivan character yesterday without using Galaxy and it worked fine.

Edit: After retesting this with completely disabled Galaxy service it turned out that the character Ivan will get locked again so it is impossible to access this additional character (even in single player mode) if you don't use Galaxy at all. Sorry for misinformation and thanks to DoomSooth for noticing my mistake.

I can't use Ivan without running Galaxy. *shrug*

Did you create an account via the ingame menu by using Galaxy once?

Ah - sorry. Did not realize that you already activated Ivan. I am not at home right now but will retry this again this evening. Maybe Galaxy in fact was running in the background without me noticing. I know that I did not lauch it through Galaxy though.

Thanks for the warning! But:
It has been requested often, but I'll just repeat it: could you please classify threads, in which you warn of de-listings, as News-threads? As regular threads they always get lost in the host of other regular threads.

Not that I personally lament the de-listing of this specific game (on the contrary), but for future de-listings of other games it would be a customer friendly service to make the warning more visible.

+100000!