Sometimes, a peck to the head is not fatal. From what I've read on these forums, some have had chicks recover from what seemed to be fatal head blows and thrive. Vitamin B-12 helps with neurological development as well as repair. Some birds that have had a hit to the head do recover, but others don't. We've never had one take a blow to the head that we know about, so my experience there is essentially nil.I had a two-day-old chick take an adult peck to the head this year and it didnt make it. I assume a vitamin deficiency is much more likely to have a positive outcome.
To your question though, I do believe a vitamin deficiency is more likely to have a positive outcome than a head injury...