If the tissue continues to retract, I'd dip it again & treat the exposed skeleton with a drop of hydrogen peroxide, dip the area clean in SW, add a drop of concentrated iodine (avoid getting on healthy tissue) & maybe a drop of anti bacterial compound. Rinse between each compound & keep the healthy polyps wet & don't take too much time. Touching the edge of the tissue/skeleton is OK but no chemicals on the healthy tissue. Caution: I cooked up this procedure myself & saved 2 scolys & an Aussie war coral this way. It's not a common treatment so use only as a last resort & at your own risk. I've read of people cutting away the exposed skeleton or fragging a remaining healthy polyp if it looks to be going downhill fast. Never done this myself but maybe others can advise on this.