yeah I'm gonna have to go with the Alliance arriving shouldn't mean anything side.
you have Madara with unlimited chakra, Meteor Spamming +wood clone/Susanoo spamming equals bye bye for the bulk if not all of the alliance.
Do you remember he was BEATING a division by himself when he arrived? The Kages told them to leave it to them.
JUUBI is a mass of chakra that spams bijudama beams and can flick away bijudama. Also did you see the size of THAT thing?! 8 Tails was a fraction of it's size when it was flicked away too!
All I see is that Obito won't let him kill everyone. Why? because if they are dead who will be in the genjutsu? Bottom line is he just wants a perfect world, if everyone is dead they can't be in it.
Rin? that is for HIS benefit, it won't really be her.
I don't see Sasuke showing up here, no yet anyway. Neither he nor Orochimaru care about this war. But then again they don't know the details either.
bottom line a lot of people should die, will they? Probably not.