Ok Those people over at bungie are pretty much gods among men. So if they are not planning on another game, they are most definitely going to use some sort of creative and masterful way to explain what happened when John and Cortana after they landed on that planet at the end of Halo 3. Maybe some weird thing with the prophets or something. I don't know but there's no way in hell they're going to leave a cliff-hanger ending like that to itself, without any explanation whatsoever, based on the nature of the bungie staff We'll see...