+1 to what everyone else said.
I have a healthy kryptonite brain that was mauled by my late purple tang, was basicly Skeleton with a bit of fleshy pieces left, a good 8 months later it looks like this
No feedings, just low flow and light,
There is still a small .5" sq piece on the edge of the skeleton that didn't grow back yet, but the rest def has.
So healing is possible if you baby it and wait long enough.