If the coral went through some hard times, I would think that the worms have moved into the dead spots to hide or to clean up stuff. If the coral is growing again then the worms will not bother it much.
You can feed the coral if the bubbles are out of if it has the feeder tentacles out. Just shoot a small amount of food through a tube between the bubbles or close to the mouth.
If a bubble comes lose from the skeleton just keep it in a place so it can't blow around.
It can start a new frag if it is keep from moving around.