Sorry to hear of your poor bird's plucking troubles. When you visited the vet, did they rule out possible medical reasons, such as poor nutrition or disease? From a behavioral standpoint, self-plucking can also be an indicator that a parrot is under stress of some sort or that your parrot is bored. Does your bird get sufficient attention and has enough toys to play with?
Regarding your question, re: will the feathers grow back, you may find
this article helpful in the meanwhile.