Yeah... CUT IT back.
I have had a few issues with coral taking a very long time to grow back over dead areas and its made a lot worse if it sits long enough to get any algae on it at all. I don't mean big globs of algae I just mean that once the skeleton turns into the brownish reddish color all dead rock takes on after a week or three in the tank.. you might as well cut into live flesh at that point cause some corals hate to grow over that. Surprisingly, some SPS do just fine and its mostly LPS that are the worst at this in my experience but its somewhat limited- .. although my Galaxia keeps adding to my experience base here and I think I am going to post it on the For Sale thread this week.....