Are we talking about what the show would be like if Ash had been written off years ago like after OS, or if he were to get written off after SuMo? Because while I doubt either instance would change the show's formula by much, I think it'd be pointless to replace him now when he's been around for twenty years. If Ash needed to leave, it should've happened over a decade ago when he first began playing the endless game of merry-go-round. Simply having him leave now would feel like a case of "too little, too late" in the sense that most fans have invested too much time in him at this point.