Andrzej Sapkowski and "The Witcher" saga have definitely benefited from CD Projekt RED's game development. I admit that I have not read any of the books, but I have played all the games.

The Witcher would probably never have gotten the worldwide acclamation that it has had were it not for the games. Sure, the games are based on the books and so there is a correlation there but if the game was not projected in a captivating way then it would have been hard to get people's attention - maybe it would have died off after the first of the three games.

Some of the elements of the original story were interesting, but a lot of it played a small role, I think. What seems to have captivated people is the unusual approach to the genre - the smallest details, the ambiance, the sound effects, the music (very big factor), and the overall pace.

I remember playing a few other RPGs that were similar like The Elder Scrolls, Two Worlds, Fable, Dragon Age, Risen, but somehow I never quite felt pulled into them like I did with The Witcher - of course this is nothing but a personal opinion.

AS a last comment, I once watched a video where Andrzej Sapkowski was asked about how he felt about the success that the game(s) had, and what it meant for him since the books were the inspiration for that success. His response was something along the lines of "well, I don't know much about that and I don't really care that much for it; I simply wrote the books and I'm not into video games". It's not really arrogance, but some disdain could be felt in his response, mainly because the event was sponsored by CDPR and because he knows himself that his fantasy would not have grown were it not for them.

Is 9.5K a bad deal?
In retrospective, yes, it was a bad deal for him. But if you take into account that he himself wasn't able to measure the potential of his creation and the creation that he would allow to become, then the answer becomes "yes, good deal... or so it seemed at the time"