Ah, I see. Weird situation for an IP. Good on them for being easy-going on it.
Offtopic, but I picked up the book series again (only read the first two bundles of short stories and Blood of Elves) and there is so much more material to use in games, makes me hope CDPR returns to it some day.
Id give it a solid 'please no'.
They've already said what they wanted to say with Geralt and friends. Returning to him at this point and continuing the story is impossible considering the ending of 3, and doing a prequel to 1 would be a retread considering they started how they did to have creative freedom seeing how they placed the start of the first game at the end of the last main novel with a time skip of sorts.
I hope they don't return with ciri, because that character is overpowered so they likely would have to nerf her and regardless her gameplay was completely different seeing her powers aren't Witcher like. Main reason would be though that with making ciri return you'd be returning other recurring characters from Geralts time, and I want these characters to retire they deserve as much after the Witcher 3.
Better to not limit yourself to returning to book characters if you can create a whole new narrative based off this rich world. Maybe a Witcher in the times they were more prominent? Or one in the future from the Witcher 3 title where the profession has boomed again?