I agree with smrobs. You would be best off I think to just roach it and let it start all over again. And I too think his neck could pull off a roach easily.
As it comes back, to prevent bleaching, use something like Quic Black - you know, darkening shampoos. Be sure to condition, use MTG, and really what you were doing before to make sure the new, healthy hair stays that way!
Cinnamon Whiskey 11 y/o 15hh Chestnut AQHA mare, 2'6 Jumpers