"I think that he's totally wrong, and that he's an arrogant motherf*cker," - Dmitry Glukhovsky, author of the Metro series
I think that really says everything about Sapkowski really. He's just a bitter old man that regrets a decision he made years ago and sees a chance within Polish law that he can take it all back.
CD Project Red however seem very confident that the grounds are baseless and if anything they'll probably give Sapkowski the bare minimum of what he's supposedly "owed" even though his books have GREATLY benefited from their success and he's probably richer and more well known now then he was before CDPR decided to even make the first Witcher game.
Also I'd like to share a reddit post I found trying to find that quote from Dmitry.
Sapkowski is being a dick, again
Apparently Sapkowski was invited to a Polish (Anime?) Convention known as PolCon, back in 2016. He had a panel there where he would talk about the books as well as the Games and he expressed heavily how much he doesn't like the games.
"The game gave me a lot of shit and stench... Because foreign publishers started to use game arts on the covers. So, some people discarded the books, saying it's not new, it's game-related. As in the book written for a game, which - especially in fantasy - we have a lot of. I had to fight a tough battle to prove, who was first."
After a question asking if the games were beneficial for him: "50/50. Obviously a little bit, because, let's be honest, there was some kind of a target, which became interested in the books after they played the games. Let's say I agree that there was a group of people like that. Except, if I start to compare it it the target that I've lost because of people who said "I'm not going to read a book about a game", I think it's going to be 50/50."
After a question about sequel to the Witcher saga, he said it's concievable, but he'd discard the games entirely, because "What do I care?" Then, when the moderator said "you don't know anything about them anyway", he said: "Exactly, I don't know. But I can ask. I know a few people who played the game, but it's not a lot, because I usually associate with intelligent people."
arrogant motherf*cker indeed.