The more I think about Palpatine’s survival, the more I like it. Here’s why:

The act of Anakin which turns him back to the light does not result in a murder. The lasting legacy of his action is that of saving Luke, not in destroying the Emperor.
Related to the first point, Anakin’s destiny is never to fulfill a prophecy. The balance that he achieves is an inward one, rather than outward.
Anakin’s overthrow of Palpatine results in him being horribly mutilated beyond what happened in Episode 3, and requires him to be hooked up to machines for thirty years in a twisted act of cosmic justice.
This turns ROTJ into a dark cliffhanger with the addition of something as simple as the Emperor’s laugh at the end of the credits.
As I’ve said before, the explanation of Sheeve’s plan for immortality makes sense of the nonsensical Sith lore and goes a long way towards explaining his silly actions in the throne room scene from ROTJ.