What is this strange happening, though rather select?  Jedi die yet only some of them disappear. Originally, we had only Yoda, Ben, and Darth Vader to look at. Ben and Yoda disappeared but Darth Vader stuck around. Perhaps this was because he was more machine than man or perhaps because he was evil.
    Now we can also look at the deaths of Qui-Gon and Darth Maul. Neither Qui-Gon nor Darth Maul disappeared. Does this mean they were machine? I think not. Or were they both evil? Well if you were to ask the Jedi Council they would probably say yes. But I would beg to differ.
    You see I think I now know what is happening with these disappearing Jedi acts. The Jedi, when they disappear are not dead but simply hiding at some grand they-think-were-dead-but-were-not party. Or something like that, and when they lay there obviously dead (unless there faking with that handy stop the heart and breathing Jedi trick, which if Qui-Gon was using must have really stunk once he realized they decided to burn him) they are in fact dead.
    Therefore we now know that Ben (Obi-Wan) and Yoda did not die. We can't really tell about Vader since they did not give us a good look at how much of him was there, assuming that the human part would disappear but then maybe that would kill him since he was suddenly at that party without a fair amount of himself.  And Qui-Gon and Darth Maul did die, unless that was a trick of Darth Maul's in which he'll come back in the next movies.