I agree that whatever the outcome of the battle-- Luffy will have nothing to do with it. Oda has a good series going that to me has done everything right and not disappointed, I can only see this fight end up as a victory fought with Zoro in charge if not taking it on all together. He did say he would never lose another fight, and that's too powerful of a moment in the series to forsake.
I'm surprised no one has mentioned the ONE (future) Strawhat that has not made an appearance yet; Brooke. Let's not forget atmosphere is completely irrelevant to Brook, so the devil fruit powers of Kuma are half as effective against Brooke. Not sure how it will all play out but I'm sure that this much is going to happen when Brooke comes back.
Lest I hope it will; my favorite moment in the series because it blind-sided me so much was when Luffy finally confronted the all-powerful Eneru and beat him. It was such an obvious and fundamental law that allowed Luffy, and only Luffy, to win that fight and I didn't see it coming at all.