No, Palpatine did NOT know how to stop people from dying, that was what he told Anakin that Darth Plagueis could do. Recall what Palp said after Anakin turned to the Dark Side: "To cheat death is something only one has achieved but together I'm certain we can discover the secret." Honestly, I never thought there was any legitimacy in Palpatine's story about Plagueis, that he was just making this up to lure Anakin to the Dark Side, playing on his fear for Padme's life. Sidious is a liar, he lied to Anakin/Vader about Padme's death and he did it for his own devious purposes.
There are so many ideas thrown out in the PT that are so ludicrously silly. The midichlorian virgin birth is one of them and that goes hand in hand with the "prophecy" that Anakin is the "chosen one". Who made the prophecy? Anakin is now Space *****? What was so wrong with Anakin simply having been an execeptionally powerful Jedi who turned to the Dark Side? That would have made the whole saga an alegory for what can happen when one allows anger, fear & aggression to rule one's life and the negative consequences that can result.
I think I'll just stick to my own original belief that all Jedi fade away and join the Force, that it was a normal thing for them, but not all can manifest themselves, perhaps that's only something that exceptionally powerful Jedi masters could do. Once Anakin had turned back to the good side then that's why he appears at the end of ROTJ, he was simply that powerful...or perhaps he had help from Obi-Wan and Yoda so he could appear just that once so Luke could know that he had, in fact, succeeded in saving his father.