There could be ways to have Vader survive. Edit out some dialogue alluding to his impending death, take out the scene with him leaning back, eyes closing, and going limp. Take out the appearance of his ghost, obviously.

It would make sense that he isn't at the Rebel's celebration. It could be left up to the viewer to decide what is going on behind the scenes: Vader undergoing repairs, possibly preparing to work as an avenger of sorts against the remaining Imperials peppered across the galaxy.

And no, don't bother to come back with some argument about "it would undermine his redemption", bla bla. He would be redeemed, but would also be atoning for his sins with the aforementioned theory.

It may or may not work. I like brainstorming on how seemingly innocuous changes mean so much for the overall story.

Whoever it was that said Palpatine isn't a lunatic but an over confident old man: You're right. You're right in the sense of the ROTJ we have now, but it's worth thinking about the implications of what would change about his character if we had him laughing like a madman while falling instead of yelling. When I posted that idea, I even admitted it would change his character. That's one of the points about the whole idea! I never liked the Emperor as a villain to begin with, but to me, if that change was made, it would make him more interesting to me personally.