Regular bristle worms are scavengers, not predators.
If there were regular bristle worms present, then they would be consuming flesh that was already dying.
Double check all your water parameters and that the coral is not in an area of too much flow.
If you do happen to observe any more worms, try to identify them with this page:
http://www.chucksaddiction.com/hitchworms.html
I suspect that this scoly is a goner, hopefully you can identify what or who is causing this and prevent any further losses.