No offence, but you're probably wrong, if you think Sasuke would stand a chance against any of the Madaras.Moreover, there has'nt been any signs of mistrust or forcefull relation between Tobi and Sasuke, like it was with Orochimaru...if you don't remember, let me help you :- While Sasuke was training under Orochimaru, he was ordered by Oro. to become merciless...Sasuke was also requested to become Orochimaru's new body...so to Oro. , Sasuke was only meant for training and becoming powerful untill the day Oro. tries to take over his body...Realising Oro's selfish ambition of immortality, Sasuke finished him...
But it was then and it is now...When he killed Oro. , Sasuke never thought of going against Konoha, but now, after knowing everything of past events and falling into darkness, Sasuke has become a true avenger...instead of following Itachi, he is following the words of Tobi...also, untill now there seems no possibility for Sasuke to join Naruto, after he had sworm to defeat Naruto and proving him wrong of his thoughts and ideas...
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Thus, if we take a thorough look in the events stated above, there is no way, Sasuke would betray Tobi...
As for Naruto, he looks completely exhausted after using bijuu dama and helping other jinchurikis...And Kurama is probably exhausted too...
So, i think there will be something when all of Shinobi army will meet Naruto, Bee, Guy and Kakashi...
I agree with you when you said the kages will loose, because it looks likely to happen... 'Cause 5 kages are exhausted and only Oonki is chasing after Hashi-Madara with will power only...
If anyway Sasuke arrives in front of the Shinobi force(currently coming to help Naruto) the situation will become worse....