On what grounds would GOG do that? They don't own the IPs of the games they sell (except for the IPs for CD Projekt Red games that their sister company owns).

Therefore, they seem to have no basis on which they could fight back legally.

Why would GOG even alienate a potential publisher?

Look at it this way:

Let's say you imported "i'crap" into the country and I bought a large quantity from you to resell them to end customers. Let's also say it was proven (for the sake of this example) that you had stolen those products. Now, you didn't have the right to sell those in the first place....

The result would be that the agreement between you and I were nullified, as a result, my "contracts" to the end customers would also be nullified effective immediately. I could en up in jail, receive a large financial punishment, and the products could be called back.

Interplay is accused of not having paid the lease money to Parallax i.e. the right to sell the games as a WHOLE to others, like GOG. With the petition from Parallax, Interplay no longer had the right to give GOG a resell contract. That contract got invalid and the games were subsequently removed from the catalog. (Well, legally it's in a state of limbo until a court rules either way.)

Now, in the states you can sue everyone over anything, so GOG could sue Interplay for foul play. However, it would be pointless. Interplay still is a publisher with other games, and even IF GOG had a slightest right to claim anything legally, it would only hurt them.

If GOG bought Parallax and its IPs, then GOG could put pressure on Interplay into better deals, money and what not. But that's purely fictional and won't happen.

The whole thing is now sadly a proxied mine field.

The team behind Parallax/Overload don't want anything to do with Interplay and the trademarked "Descent". You can imagine why the team behind Overload and the team behind D:U don't collaborate, not to mention they each went their own way. D:U has rented the name from Interplay but it is a DM-mix between Q3+UT+Descent in designed buildings (not hollowed out caves).

With every respect to the creators, they've really made a fun and unique game, I just quite honestly don't think it actually deserves the name. The naming should have been the other way around. Again, just purely fantasy.

A contract to sell and distribute their IP, yes. But it's still their IP. If GOG/CDPR was in a situation where they co-developed or co-owned the rights to the Descent IP with Interplay, they might have some grounds to fight a demand from Interplay to cease selling it. But even if they were, they wouldn't want to jeopardize a relationship with a major publisher.

Does it matter who owns the IP? A contract is still a contract and business is just business. Why would a publisher get personally butthurt towards GOG if GOG tried to fight to keep some games in their catalog?

Of course it does. I can't enter into a contract with you to sell you the Golden Gate Bridge because I don't own the Golden Gate Bridge.

There is a huge difference between GOGs and real estate. And the owners of the IPs do agree to contracts with GOG otherwise GOG wouldn't be able to legally sell GOGs in the first place.

The contract between the IP holder and publisher might not involve GoG in any meaningful way. It's up to the publisher how to distribute and making contracts with game download sites and such. While the contract with Interplay might still say GoG is allowed to sell the game - if Interplay has breached their contract with the IP holder and lost the right to distribute the game then GoG can't sell it without violating copyright. If the IP holder notified GoG of the situation and GoG keeps selling despite notification otherwise - should the courts side with the IP holder against Interplay GoG may become legally liable. The ramifications of such generally isn't worth it (may even include forced removal of all games from accounts - the PR hit alone is terrible*).

*Almost happened to Colin McRae Rally. The "publisher" didn't have rights to distribute the game in the first place. The game was tentatively going to be removed from everyones accounts. GoG must have come to some kind of deal with the IP holders to prevent that from happening.

...they are contracts that allows GOG to sell the IP owners' products. Those contracts don't give GOG any kind of ownership or control over those products, beyond the right to sell them and keep some of the profit.

For example, GOG presumably has a contract with Disney to sell Star Wars games here. That contract gives GOG the legal right to sell Star Wars games. It doesn't give GOG the right to exert its own autonomous control over when/where/how it can sell Star Wars games, especially if Disney makes the decision to pull them from the store.

You should differentiate the written laws, unwritten laws like common practices and wishful thinking.

IPs can loosely be split into separate domains like access to a computer or documents;
1. Only allow read / use the product (end customers by common EULA's)
2. The right to sell / redistribute a product (Re-sellers like Interplay / GOG)
3. The right to change and total ownership over a product (Parallax or the original creators)

Problem is, in Descents case the IPs are fragmented even more as no one owns the whole IP:
1. Name "Descent"
2. Game assets x
3. Game assets 2x
4. Game assets 3x
5. Leasing right (Parallax -> Interplay -> GOG)

We're talking about limited right here, and no, there are no differences in written agreements between two parties, be it leasing, renting or buying digital or real objects.

Every agreement/contract in our society is based on limited right.

If you rent a car for only 10 days then you are limited to only 10 days use and don't have the right to sell it or rent it further, if you buy the car you have the right to sell it, rent it or use it as long as you want to privately, EXCEPT setting up a re-sell company and using the manufacturers / re-sellers name or rename the car to your own liking, or drive wherever you want, no matter the type of the car. In short, GOG had a nr 2 agreement with Interplay with its own limited right, assuming that Interplay had been given leasing right from Parallax. That didn't include to do what ever they wanted. Why would GOG choose to get bad reputation, alienate potential partners new and old, and loose revenue and costumers?

GOG could have been held legally liable if they violated that non-right by not complying with Parallax's petition and not retract those games, even if the status was/is murky.

Descent is BACK!

HELL YEAH!!!

When did the games go back up and what are the odds they can go down again? Since I bought all three thanks to the sale, I get to keep them, right?

3 days ago.
Nobody knows. The first removal came completely out of the blue.
Yes. Even if they are removed again, you'll still be able to download them.

https://www.gog.com/news/welcome_back_descent_series