It could be Tom Riddle, cause Rowling even mentioned that certain events coupld have been switched around in 2 and 6. As well Tom Riddle is not Voldemort--at least not yet, there may be some kind of past ressurection...
If it is Dumbledore then that would acknowledge his indepth knowledge of magic. Yet it would seem probable that Dumbledore may dies because he is not the one who is supposed to fight Lord Voldemort, and knows that as well, so he wouldn't mind sacrificing himself to save the wizarding world...