Is neuronal demylenation due to B12 deficiency reversible?

Partly. Good question from a med student. Vegetarian's myelopathy is all-too-familiar and it regresses at least some. Here's one of the unlucky ones: http://www.Ncbi.Nlm.Nih.Gov/pubmed/17616346 forgive me, but i can't grant any moral high ground to someone who paralyzes himself.
Not in 2014. With current knowledge and techniques, no. Perhaps in the future.