I actually thought of a really good theory, and it somewhat has to do with genre trope. I don't know the exact trope but I like to call it the experimenter trope. A person who changes stuff to what happens;With little to no interference. Now how does this trope fits the M.O.M? It's simple. I looked at key aspect that he follows the trope. He created the book of prophecies of an future war to start the 1st keyblade war. He created a "lost" page to cost disruption of the foretellers. He told Luxu something that causes him ask why, and only with you'll see. Leaving us in the dark till KH3. Now I'm taking a big stretch so hear me out. I think M.O.M. didn't want Luxu to have a copy because it will rule the experiment, and may backfair. Remember Luxu is probably the most innocent of all the foretellers. In X Back Cover, I can see in someway Luxu is caught in the middle. To carry out and look after the events of the 1st keyblade war. Now I bet your wondering, where does this all fit in with him getting his keyblade? I think the answer lies within ventus, and marluxia somebody. Not them directly, but how they are still around to present kingdom hearts. Till Union cross reveals how they are here, we can only speculate. I believe it's possible M.O.M. is still around, and watch current events through the eye of No Name. The only evidence I got, and not even the best is that he can use No Name to see into the future, and Master Xehanort can't. The reason I say this because to me, that means at some point he will get back it. Still working on the kinks to that part, but it's sufficient enough. Before I finish my theory, I do think it's plausible for M.O.M. because ventus is here, and that makes ventus is older than xehanort. Hopefully we will also get how xehanort met ventus in the 1st place. Hope you enjoy the theory, and give feedback/corrections while you guy's are at it.

This is an interesting theory, and while something like this may happen, it would kinda make Xehanort irrelevant, and the whole point here is that the entire saga we've been playing through is called the Xehanort Saga, and as such, I'm sure he'll remain the focus till the very end. I don't expect the Master Of Masters to just pop up and say: "Well, you're the apprentice Luxu deemed worthy! Thanks for your time, but I'm gonna take that Keyblade from ya!" When he said he was going to disappear, I think he meant it. Maybe he could have discovered a way to bring himself back, but I think it would be preferable if he was the antagonist of the next saga, ya know? Let Xehanort have his final moment in the sun before being defeated by Sora and friends! Then the MoM could have his way after that, ya know?