By the power of truth, I, while living, have conquered the universe.
Posted by: Videofreak63
there really is too much information to make a clear ending. I doubt that it's in an alternate universe, because slipspace is just another dimension that they used for travel, so it may have put them in another dimension... but then there would be no mars, or earth... and we probably would have seen it in the episode origins in halo legends. As for the flood, their is still a chance they survived as well. They made it out of the galaxy 100,000+ years ago when the humans found a cure, only to return to battle the forerunners. The planet seen in the final cutscene is most likely onyx or another one of the shield worlds used to protect against the flood, or hell it could be one of the 500+ other forerunner worlds.
You were doing great until you mentioned Onyx, which - conveniently enough - was destroyed. -_-