I agree that Dumbledore had to leave the picture in order for Harry to mature into the Hero that he needs to be. it makes excellent story sense. I see enough clues that may indicate that he has faked his own death (including him telling Draco that they could fake Draco's death to protect him, right before it happened), that I would not be surprised if this is revealed in the next book. I would hope that it would happen toward the end so as not to interfere with Harry's maturation process though.