I've been down this particular pike a few times with dents in shotgun barrels. I doubt the methods would apply (or the tools available OTC), but with shotgun bores a skilled worker can remove dents from the inside. Worth a chat with a good shotgun mechanic, but I wouldn't be 100% optimistic by any means. You just might be stuck in wallhanger land unless you can find parts. It's certainly not a "collector" in it's mangled state, so gunsmithing could at least turn it back into a shooter.