Before you go buying a replacement... try taking off the windscreen and using a broomhandle (rounded end) to push the screen from the inside out. Most times with a little muscle you can get it pretty close to the original shape. Use finesse as not to tear the screen.
As for sound characteristics... Sure, maybe a very small difference would be noticed, in the most critical listening environment (proximity of the screen and foam to the mic element. Unless you managed to damage the working elelments, which is doubtful). But for home recording and/or stage, I seriously doubt you could tell. Even in a critical environment, you never know.
Just last week, my band was tracking some new material. Our singer was getting frustrated with the vocals on one particular track. Sound, performance,... it was hard to finger. We threw up the 58 he uses in rehearsal, with a U67 placed behind it. Letting him sing like he's used to, with the 58 essentially a prop. (Not a new trick, I think the idea came from "Behind the Glass", I wish I could remember to give proper credit)....
You guessed it, that beat to hell, crusted with who knows what filth/funk, 58 gave a signal that worked on that track. Sat in the mix and just felt right. Obviously I am not suggesting that a 58 is better than a U67 (wish I had one at home).. but in this case it worked, dents and all. Don't worry, your 58 should give you many more years of great use.
