I totally agree with him getting to the point he is ...

BUT, if he is STILL a total wreck (understandably so) ... DON'T take him on the mission that is your "one chance". As it is .... Rocket does everything useful on that trip anyway. It probably would have gone better with JUST Rocket anyway.

Plus ... look, it's a super hero movie ... while I believe that real depression in real people in the real world is not a "just snap out of it" kind of thing, real people in the real world don't wield hammers made from the heart of collapsed star EITHER, and Thor can do that!!! So have him Snap out of it ... have him clean up and sober up and man up and get back to being a Hero and not a blubbering waste in a short time (shorter than real people..., you know, like in 5 minutes of Movie Time).

I guess they kind of have him do that in the battle ... suddenly the beard is now braided, and his eyes glow with lighting again and he fights Thanos ... Have THAT transition happen before "the one and only shot" mission.