I think they will regrow but repelling the deer is the only way to save them long term. Deer are browsers. That means they take one bite and move on. You must have a pretty good size herd. Also, once they find food in one spot, they will continue to look in that spot for food. Your Hostas might be doomed! Have you tried a scarecrow rainbird? I keep the deer out of my veggie garden with one but the deer never got into the habit of eating in that area in the first place. My roses, on the other hand, are stripped bare.
I found a youtube video testing it but can't find the link on this silly little tablet. Anyway, they work. The only suggestion I would make is that to hold the Scarcrow still, I had to plant it in a plastic pot buried in the ground and full of gravel. It has such a violent startup that it was literally throwing itself out of the ground.
Daisy