Yeah, even with Madara defeated, I don't see the manga ending just there. To me, Orochimaru just isn't the guy who is going to change just like that, and live a life of peace which means giving up the ambition of learning all forms on ninjutsu and practically becoming a god which was why he wanted Sasuke's body. I don't see how Orochimaru could take over Sasuke's body at this point, since both Naruto and Sasuke are practically demi gods, but I do feel he will do something out of the ordinary to achieve this goal. Who knows, he may even try and take over Madara's body if Naruto and Sasuke are able to weaken him to that point, and then also there is the Sage of 6th paths mother who has to play some sort of a role in this series, considering she is the most powerful character there is.