Kylo dying was trite and cliche and also completely predictable given that it was Disney. But having him alive, alone, living forever with his crimes…that’s more interesting a fate.
I personally believe it wouldn’t be necessary for him to be completely alone. I see him trying to start the Jedi again with Rey at his side, but obviously the galaxy wouldn’t see those Jedi as good people as a result (especially if it somehow leaked that Rey is Palpatine’s granddaughter). I see that story as pretty interesting, where the Jedi have to prove themselves to be good.