I am guessing that they will survive, but will never be all that attractive. Actually, they will most likely look awful for the near future. I would suggest ripping them out and replacing them. But first find out if it was in insect or disease that caused this. I worked for one idiot many years ago who took his dull, rusty hedge trimmers, poured motor oil all over the blades for a lubricant, and then trimmed away. Did an amazing amount of damage to an what once was a beautiful shrub.
Do a thorough inspection, take a cutting of some dead and live parts and send it off to your local ag. extension service. They might be able to help. You don't want the same bug/disease damaging the new stuff.