I'd probably straighten the cage and replace that broken in half derailleur hanger, if it won't shift correctly after that just replace it.

In a perfect world you would just replace that derailleur because undoubtedly there's some little problem somewhere, those things can be touchy. But in a practical sense just eyeball it the best you can and zip it right back on, see how it goes. If you have persistent problems, you'll know to swap it out quick.

I've muscled mine back straightish multiple times. Good as new.

Other than straighting the derailleur arms back again and checking the derailleur hanger alignment just in case I think it's fine, those non-gazillion-sprocket derailleurs from back in the day are quite sturdy. We all do stupid things voluntarily or not so don't be worried

I would replace the derailleur since straightening any part of it that's bent probably won't work that well and buying replacement parts is probably as expensive as replacement if this is 10 speed or below. Can't say anything about the chain without inspecting every link. Need a new derailleur hanger of course and for someone to ensure it's straight.