Re: damaged wrestlers
I've been through the training as a wrestler. While I never did a top rope elbow drop, I have done standing ones. In my opinion punk has been able to do the elbow drop in a safe way for him and his opponent. Where I trained the mat didn't always have a lot of give to it, while I never bumped in a wwe ring, I'd imagine that they are built a lot safer than any ring I've been in. I would be pretty surprised if punk hurt himself on the elbow (with the exception of someone moving, slips etc.)
As for who is too damaged to get any further. I would say any of the old WWE veterans who keep re-doing their gimmick for local crowds. The ones in their 'greatest hits' phase. People like val venis, x-pac, billy gunn, godfather etc. Not to say they can't be road agents take a look at road dogg. But based on their age and everything I highly doubt they'll ever get past the stigma of their established characters.