I haven't given this too much thought, I don't know if it has been said again in this forum or not I just came up with this and want your thoughts.
It may be stupid, but since it's me it most probably is not.

It is as far fetched as it can get though. So here we go:

Maybe after Sasuke gains the Rinnegan ( this is an assumption needed for my theory ) and the two villains are somehow defeated (don't ask me how) Sasuke will join the good guys' side (see? far-fetched) and team up with Naruto.
Those 2 together would be by that point at Sage level correct? I mean Sasuke will have the Sage's eyes and Naruto I think already has the Sage's body and sealing techniques and chakra control.
So these two together can tame the Juubi (Sasuke's part) and then extract and manipulate its chakra (Naruto's part) to divide it once more. If we assume that Naruto who is very familiar with each beast can sense each one's chakra then with a little Creation of All things (Sasuke's part again) the 2 of them can reform the Bijuus.
So this way the Juubi can be defeated.

What do you think? :P