Obito would not have had the Kyuubi's chakra without Kabuto summoning the Kin-Gin brothers. It would have just been Obito, Gedo Mazo, and the zetsus vs the 5 nations. Naruto would not have sensed the 9 tails chakra from the brothers, which lead him to find out about the war, so Naruto and Bee would have stayed safe within the barrier.
It can be argued that Obito could just revive Madara, but if he could do that than what was stopping nagato from reviving Yahiko. And don't tell me that it is because he thought it would be immoral or something like that. He animated his corpse by shoving chakra receiving rods into his body.