Although Geralt of Rivia's story has been concluded, CD Projekt RED is open to more Witcher games--they exclusively own the rights to the franchise after all.
CD Projekt RED is currently working on three projects: its monetized free-to-play multi-platform card game Gwent, its insanely ambitious high-tech masterpiece Cyberpunk 2077, and a mysterious new unannounced triple-AAA RPG. What if the latter is another Witcher game?
At CDPR's 2016 yearly earnings conference, Adam Kicinski answered a question about The Witcher 4. Is it possible? Is the series dead? "The Witcher was designed as a trilogy, and the trilogy cannot have a fourth part, can it? We like this world a lot. We've invested 15 years of our lives and a lot of money into it. So...we'll think about this," Kicinski said during the conference.
"We're rational people. Sometimes we have some strange ideas but we are rational people. We have full rights to the Witcher games and they belong to us. We put a lot of money into promotion and the brand is very strong. So...you'll answer your own question."