fish are tougher than we give them credit for.
I had almost the exact same problem with a 11" silver shark, it got stuck between some artificial coral and in the process of trying to wiggle free, took several large chunks...and I mean chunks out of his body and head. It look so bad, I couldnt grip him and had to use a towel, he had a large '10pence' size hole across his head, and similar chunks around his body. You could see right inside him...gross I know!
However, with plenty of water changes and good water stats, over the next week, he healed up really well and is now back to normal...well, he has a lil dint in his head. But no abnormals noticed, so all seems well.
Another story...if I may, to give you an idea of how tough some fish are: a friend of mine has a friend in Italy. He says on a certain day there is a market, and people turn with plastic carry bags for the fish, trout etc, they buy the fish, put it in the carry bags...no water...just the fish...still alive! they then walk/get the bus home, and put it in the bath with water until they are ready to cook it.