The Witcher refers to Geralt. A witcher refers to the rest IMO.
Plenty of stories to tell in that world. With or without characters from the books or the games.
Might not even involve a witcher as main person and might not even be an RPG. The time of the spheres could make an interesting game.
Dandelion's adventures or Yennefer's story might make great games too and only have witchers as side characters. Geralt could have a cameo in them.
As far as witchers goes, Vesimir and Lambert are interesting characters, though Lambert is still a youngster. Especially Lambert's constant comments would be a nice edition.
We'll have to wait and see, but I seriously hope CDPR returns to this world.