They should grow back. If it is bacterial or fungal, you should see a film/growth over the scaleless area. My advice for now, is to make sure you keep up with PWC
and keep the ammonia and nitrites undectable
Post back if anything changes.
Another thing you can do is post on a goldfish oriented site (find the top ones on aquarank) and ask for a second opinion. Never hurts to get a second opinion, especially since so few of our members keep goldies.