I a few years ago my peacock Alto had what looked like a bite wound on his neck (probably a raccoon) and the feathers in that area were gone. It took a while but eventually it filled in.
I am not a pheasant expert but I do know that pheasants can be really prone to feather picking or even cannibalism. Something you might have to look into is using peepers or bits or something that prevents them from feather picking. I have even seen a nose ring on a green peacock before to prevent him from feather picking. I would keep a close eye on the peahen to make sure she isn't also picking off feathers on the peacock. If she is she might need to wear something on her beak. I think the feathers will grow back since this is the first time this has happened, but if this happened say every year I think eventually the neck feathers might never come back.
As for his train you probably will have to wait for next year unless if some of the train feathers have been pulled out completely. Again with my peacock Alto, some of his long butterfly feathers got pulled out early in the breeding season last year and he re-grew them throughout the breeding season. Then it took him a while to shed those since they were newer.
