He’s so popular with fans Diana Gabaldon wrote a whole series of spinoff novellas about the character.
Lord John Grey’s a very popular character in the universe.
Over time, there have been rumors about a spinoff series and more.
I can’t imagine the writers would simply want to cut out the character, but with no news about a scheduling or money dispute it’s hard to tell why this is happening now or if perhaps the character will actually be brought back down the line, but there are no plans yet.