I can't feel that bad for him. I understand that he made a bad deal, but it seems he hardly made an uninformed one. He had no faith in the success of the games and decided that he'd prefer to take a (in hindsight, very small) lump sum. Since then, CDPR has, through enormous talent and labour, created an absolutely outstanding series of games based upon his works, and received surreal amounts critical and financial success. The games also are not direct adapatations of any of his work. They do not retell any of his stories. He will be the first to tell you that the games are not the place to go if you want to hear the stories of The Witcher, Geralt. They are the inventions of other authors, at CDPR, working using elements of his work. Those are his own words, paraphrased. I feel then, that whether they'd created Witcher games, or some other series. CDPR's success is their own. at most, the license gained them some early success for their first game. But by the time of the second game, I think it's fair to say that the games had fully come into their own right, and have on their own merits, and through the labours of CDPR, become a more visible, successful representation (if a false one, as he will remind you) of those characters and that world. So I do not feel that they owe to him a great deal. I find the idea that CDPR owes their success to him a little silly.
At the same time, I do not mean to say that his works or fortunes have languished as CDPR's star has risen. I do not know what the sales figures are for his books, but The Witcher has become something of a household name the world over. I would be extraordinarily surprised to hear that the game hasn't contributed tremendously to the success of his books. I rather suspect that his upcoming Netflix show would never have happened had the games not come about and been so successful as they are. I feel, then, that he has benefitted greatly from CDPR's work, even if not by direct financial compensation. This is perhaps the best bad deal he could have hoped to make.
None of this, of course, has anything to do with what the law says, or what the ultimate decision may be, in settlement or in court. In this whole situation though, I do not feel the least bit bad for Sapkowski, or the heads of CDPR. If there is a party who has not been duly rewarded for the success of The Witcher games, I think it's the regular employees of CDPR who have brought CDPR and Sapkowki's vision into reality through their tremendous labours, and are, as I understand it, not being compensated exceptionally well. Neither here nor there, though.