The game was a module I was running that was meant for Thor and in the module it said that Thor couldn't bring in Mjöllnir. There were some runes or something that prevented it being taken in. This was my adaptation of the module that the player just like Thor couldn't bring his hammer in.
As it has already been said. It is rather common in the genre to lose your powers. But even without his powers he wasn't as useless as sticking his nose in the air and pouting. He could still punch, kick, throw, and get the other weapon that is already in the cave!
To not even try to be hero because you don't like the situation is juvenile. I'm going to be a jerk because I think you are being a jerk? How old are we? My friends and party members are getting their ass kicked so what do I do? I protest because life isn't fair and I won't be as useful.
Get your whining self in the cave, remove the sword from the rock, and go kick some butt! Guess what the sword would have given your powers back and made you super strong but you don't know that because the character decided to not even try. That is my fault? There were enough clues.
My point is you don't know if you don't try. Pouting about it not being fair will accomplish nothing.
Another thing that is a theme of the comic genre is to rely on your friends and team members. He decided to not get by with a little help from his friends. His choice was to sacrifice the entire team for a concept and felt justified because that is what his "hero" would do.