Duncans are remarkably resilient. Unless they're right back to the white endoskeleton, just give them some time. I thought my very first was a gonner after it 'melted' overnight. 3 weeks later it started regrowing from the central depths of the corallite. As for 'heads', I've had 3-4 cases of polyps (palys, mushrooms, and a riccordea) upping shop and moving around the tank. I hear it's a panic response, so.... my bad? But it worked out, they're all healthy and happy in their new homes. My philosophy, let them go where they like.
Below photo is 3 weeks (22 days) after 'melt'. In this time the outer membrane remained green, and the skeleton of the septae were purple and appeared mucus-lined.