They don't look like "chicks" when they're hatching - especially in this type of situation. No, I wouldn't think it would have started hatching if it wasn't ready. Although, the smashed and dented egg isn't how eggs hatch. It makes me wonder if somehow the egg was smashed by the hen or something.
That said, it's been so long in this situation that it may be too weak to get out.
I found a chick left behind from our broody that was trying to hatch. I panicked and pulled it out of the shell -- it was just as "horrible" as you're describing. It wasn't ready to be hatched and just laid there. I thought for sure it would die, and after a while I turned the heat lamp off. Much to my horror, I noticed it moving about an hour later. I flipped the light back on. At some point I gave it some Nutridrench because I knew it lost blood during the hatch. It took days, but that little chick pulled through. He ended up back with his hatchmates and lived happily ever after.
I guess the questions is how involved do you want to get? I think you can leave it under the mom and let nature take its course. It may hatch. It may not. You can also try to hatch it and see what happens. Unfortunately, it may not make it either way.