I had one of my silkie/Orpington girls get scalped by one of the other chickens recently (we think it was one of the roosters, one's a horny little crap and she's the most passive of the hens). she wasn't quite that bad (but it was still pretty bad) but I took her in, put her in a pet carrier for a while, treated the wound with some salve for the first few days, switched over to a wound spray, and after a while she started perking back up and looking better, it even looks like her skin is at least trying to grow back.
she's managed to perk up enough that I had to move her into my bedroom so she doesn't fuss about not having company. and starting tomorrow she's getting blu-kote instead of the other wound spray and I'm going to start slowly working her back into the flock.
so there is some hope, just keep an eye on her and make sure she's not suffering too much from it. chickens can be pretty resilient. heck, I had a chick years back that had most of the skin off their neck and upper back pulled off by a blue jay that managed to survive and thrive before.