Bringing back Palpatine in order to allow Ben Solo to recapitulate Vader’s sacrifice from ROTJ in order to once again kill the very same being would make the ST feel pointless. It would seem that ROTJ’s ending was broken down to be kicked a couple movies down the road and then redone.
If they have to bring Palpatine back, I hope it’s a vision or something rather than a true post-mortem consciousness. If Lucas had any say in it, I doubt that’s what would happen.
I really don’t think they’d go that route though, since it is so pointless.
Maybe Rey gets possessed by the spirit of Palpatine and Kylo has to save her.
Maybe the McGuffin is that they have to find the first Sith temple, where Palpatine is reborn.
Or heck, maybe this is the movie to introduce literal time travel to Star Wars so that JJ doesn’t have to write a true ending.