The tank looks awesome.
Sorry about the coral. It's in pretty rough shape but you never know, it could turn around. I guess it depends on what caused the stress and if it's able to overcome that. I have the same thing going on. Just randomly pieces that were doing really well, will suddenly succumb and look like that. The holes are dead polyps or basically what's left after the polyp is gone. I have had 3 frags this week alone that suddenly declined. I'll probably lose them all.
Good luck.