I think the ending would be Madara will be the host of the 10 tails. Naruto and Sasuke will fight but they would soon realized that they need to team up against Madara. But each of their power and skills would not be enough to defeat madara so the two of them would use the Ultimate Jutsu "THE FUSION" which they have discovered from an ancients scroll of the Rikudo Sage. Since naruto is the descendant of the Son with the Sage Body and Sasuke is the descendant of the Son with the Sage Eyes so they are the only compatible and capable of performing the FUSION making them both a one person, The Sage, as prophesied.