I have had worse scalped chickens make it. There was gamefowl rooster I found running down the road in the rain years ago. He was exhausted, scalped, his right eye was swollen shut and the lid bulging with infection. I caught him and took him home to heal him up. Here's what I did for the scalp healing.
There are two species of medicinal plant, both often referred to as Plantain. They possess excellent antimicrobial and vulnerary properties (a compound called Allantoin in them causes increased cell growth and division, resulting in faster healing of wounds). Either of the species' leaves can be ground into a paste and placed on the wound. By itself it will not stick for long, so in the case of needing to use it on the head of the rooster I cut up some soft, stretchy underwear (like many women's underwears are) and fashioned a little "cap" I could tie under his chin to keep it in place. (I used a different protocol for the eye which is irrelevant to this discussion). You could use other materials, like stretchy leggings or panty hose.
These plants are super common around human settlement, and unless you live in the desert there's probably some growing within 500 feet of you.
Plantago major ("Broadleaf Plantain")
Plantago lanceolata ("Ribwort"):
The scalp skin grew back and did not become infected. It took it a little while after his skin had grown back in before the feathers repopulated, but amazingly they usually will.
I don't have any photos of the original wound unfortunately but here is a photo of him post-Plantain treatment before his feathers grew back in. The skin is completely regrown here:
And after feathers have regrown:
If you are unable to get ahold of or don't care to use antibiotics, this is an excellent and free option. I use it on myself all the time, other humans, chickens, ducks, dogs, geese. It's wonderful stuff.
Hopefully the hens pecking him did not cause brain trauma. If his pupils are dilated and/or you suspect brain swelling, a compound in Dandelion leaf (I forget the name at the moment) crosses the blood-brain barrier and works against brain inflammation (unlike the vast majority of anti-inflammatories), though nothing I know can undo already caused brain damage; this is simply a preventative so that swelling does not cause more. This is fed to the chicken. I've used this to treat Wry Neck successfully.
I wish you and your rooster good luck in the healing process.
