I think we all know that Madara will eventually come into contact with sasuke. This was confirmed by Kishi when he sais naruto & sasuke will meet at least once during the war. My feeling is that obito will already be defeated by that time. The ten tails might be broken up again thus preventing madara from becoming the juubi jinchuriki, so that leaves madara as the final villain for the war.
What will madara's reaction be to sasuke. Probably compare him to Izuna. omehow I'm getting a feeling that sasuke will seek out power from madara to get him ready to fight naruto. What do you guys think?