CD Projekt RED on Why The Witcher 3 is Geralt's Last

In case you were wondering why The Witcher 3: Wild Hunt will be the last Witcher game to feature Geralt, IGN has asked the question to CD Projekt RED's senior writer Jakub Szamałek and came back with a sensible and straightforward answer. After three games, the folks at CD Projekt felt this was the right time to put a cap on Geralt's adventures:

(I think good stories must have an ending. You cannot extend them indefinitely, and we felt that Geralt has had such an amazing adventure, and his saga is already so long and complex that this seemed like a good point to think about an appropriate finale for the story.)

Geralt (has reached the end of his journey,) but this doesn't mean it's the end of The Witcher universe in video games. (The Witcher universe is a very big place with a lot of NPCs, a lot of characters, a lot of places we haven't shown yet,) Szamałek said. (So, we might return to it at some point.but we think that this is a good place to let Geralt enjoy his retirement and try something new."