Maybe that's what he does. Who knows, perhaps Madara has stored Minato's body in some location, and will use it again when resurrecting the Jubi. From what I remember, Konoha never found Minato's body after he died sealing the Nine-Tailed Fox into Naruto.
But that is an interesting thought. I have another theory as well; in order for tailed beasts to be sealed in the Demon Sealing Statue, it is best that they be extracted from their host.
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Yes, there is an exception with the Three-Tailed Beast, but in this statue, the Nine-Tailed Fox must be sealed last, or the statue will crumble. Having said this, did Madara purposely let himself be defeated by Minato, so he would gain the oppurtunity to seal part of the Nine-Tails' chakra within himself, and the other in Naruto? Consider this - it would take a long time for Akatsuki to capture all the other beasts before the fox, and Madara would have to keep it under control until the sealing of the Nine-Tails comes. I'm sure that would be difficult if not impossible to do, so to ease his work Madara played himself off weaker than he really is so Minato would do exactly what he wanted.
If the Nine-Tails were not to be sealed that night (and destroyed Konoha, speaking hypothetically), then Madara would have to restrain the fox for many months, if not years, until they would finally be able to seal the Nine-Tailed Fox. Somehow that just doesn't seem likely. Minato said himself Madara would not be able to exert control of the Nine-Tailed Fox for very long, so perhaps Madara gave Minato the oppurtunity to seal the fox so he could come back for it years later. Madara himself said "someday, it will be mine again." Each time Madara discloses part of his plans, he always emerges with the intention of carrying out his words. This is a theory of mine, and it might be wrong - but if Minato did indeed defeat Madara, it would not explain why Minato had such a helpless expression in chapter 440? The word "everything" in "back then...he saw through everything I did," would not be the correct choice of words then, now would it?
Of course, I do not doubt the fact that Minato probably defeated Madara, but I just wanted to hear everyone's opinions on my theory. Thanks.