I think it will be because heroes always win. Thanos will have the power of God so how can he lose? He can actually make every Avenger and hero pop out of existence. If he has all infinity stones he doesn't even have to lift a finger. Even without the stones he can take on most of the Avengers. So if the heroes win and thanos ends up in some type of prison all that build up would be for nothing.
Most Helpful Guy
I loved all the avengers movie so I don't think it will be a flop.0