We had a chicken attacked by a dog 4 months ago. It looked way worse than your photos. Our neighbor is a vet and she came over to inspect. We flushed her with water to clean and she gave us antibiotics to crush in liquid and feed with a syringe. There was little we could do other than wait. Her entire neck was showing muscle. Our neighbor assured us that chickens were extremely resilient, so we decided that as long as she had the will to live, we would help her. We hand fed her through a syringe (yogurt with water and similar things) for two days, then she started eating and drinking by herself. We bandaged her initially, but realized that she couldn't move her neck freely and it affected her balance. We removed the bandages and were amazed at how quickly she regained balance and will to live.
We kept her in a large dog kennel in the house for three weeks. We even let her out to walk around in the hard-floored areas and exercise her wings. The main reason for keeping her inside while she healed was because the other chickens would peck at her and possibly kill her. The biggest problem was re-introducing her to our flock (only 5). We chose the friendliest chicken to come inside and stay with Nutmeg in the kennel for a couple nights. They both seemed very happy, Nutmeg especially having company once again. We started letting her outside during the day with the flock, but kept her inside at night for a few more days before we felt sure that she would be safe. It did take a couple weeks of her being run off by the other birds, but she re-gained her status as an equal. She will never have feathers on her neck again, but she is a happy, productive flock member (it took several months before she started laying again - she had lost half her weight). We think the lack of feathers on her neck give her a 'decorative' look. You can't even tell unless she's standing up stretching out her neck. She really deserved to live and we're glad we put in the effort to help her, even though at the time we were feeling a big silly because of our devotion to a chicken. Lessons learned:
1. Antibiotics
2. Chickens can live though a lot
3. If they have the will, it doesn't take a lot from us humans to help them live
4. Re-socialization with the flock is key