when palpy tells ani that only one has cheated death i originally assumed he was referring to a previous sith lord. after rewatching the movie today i now feel that he was referring to qui-gon. somehow palpy determined, as did qui-gon, that someone could exist forever within the force. unlike qui-gon palpy obviously hasn't unlocked the key to this ability.
with this interpretation it makes palpy into a liar when he tells anikin that the secret to saving someone from death can't be taught by a jedi, since only qgj (and later ben & yoda) learn it. how and why ani becomes a spirit at the end of ROTJ are completely open for supposition.