As long it has stopped receding or if it was from a sting from another coral or something like that and the corals has recovered it will eventually grow over it again but it might take a while. If it is RTN or STN you are better off just fraging a good piece.
If it is dead, I would cut it unless it is a thin-branched deepwater. I like to leave those so long as algae doesn't grow over. They often die back in the wild and a well-known importer gave me that advice. It has turned out to be good advice based on my experience. If it is just bleached and the tissue is alive but devoid of zoanthellae then don't cut it but do try to lower the light level a bit to let it heal.
plus one on lower the coral in the the tank. Then slowly raise it up until you find the sweet spot. I have seen some sps come back with very little tissue on it.