"There may never be a Witcher 4"
Um, why would anyone EXPECT there to be? Witcher 3's story closes the book about as conclusively as you can in a non-linear story. Shit, it's entirely possible for Geralt to officially retire at the end of that game.
Sure, maybe at some point it would be interesting to revisit the Witcher universe, but the character and his story don't need to be a part of that.
I thought we were all clear that the guys over at CD Projekt Red are cut from a different cloth then all these other hacks running their franchises into the ground with sequel after pointless sequel.
In the modern age of expansive cinematic universes and long running TV epics, it sometimes feels like it's been a long time since a large scale story actually ENDED, but let us not forget that, in spite of what Hollywood would have you believe, endings are a natural part of a story's life; when it's time comes, a good story knows how to die with pride.
The story of Geralt of Rivia has a perfectly fine ending as is; it's over, leave it alone and move on.