Cinny, they are surprisingly tough. Dogs are hard on them, but I have had several that were fine after my neighbor's dogs got after them. The stress of the attack seems harder on them than anything. Years ago I had one that went into the back yard with my dogs. By the time I got to her they had plucked her under the wing and torn a flap of skin away. It looked horrible. I washed it out as best I could and smooshed antibiotic over it. The next morning I got her to a vet and had her sewn back up. She looked so horrible right after the attack that I thought I had lost her (she also was a favorite). The next morning she acted like nothing had happened. The vet had to completely pluck her side to stitch her up, so she looked like a Frankenchicken until everything grew back in. Pooh ended up living for five more years and was one of my best layers and sweetest hens. She layed a mint green egg that was gorgeous.
Have hope. They seem to sometimes weather the worst.