What would've happened if Obito didn't accept Kabuto's help?
I guess Obito will lose the war.

Obito seems to have underestimated the 5 nations. Maybe because he thought that he can take advantage of their previous wars and conflicts and never expected that the alliance will truly go in war as one allied shinobi rather than fighting for their own nation.

As for plans on resurrecting Madara, I don't think he still plans to do so since he said that he wants Nagato to use the 7th path on him and his current actions shows that he wants to be the Juubi's jinchuriki himself and the one to cast infinite tsukoyomi and I think he underestimated Madara on that one too.