I doubt your star tried to consume a bristle worm. More than likely, your star is dying and disintegrating on it's own, and the bristle is cleaning up the mess.
Why your star is dying would determine whether there is anything you can do to save it. These stars generally die form one of two causes - 1) the are acclimated poorly and they "fall apart" within about 3-4 weeks of entering a a tank due to osmotic damage, or 2) they starve to death and begin falling apart (this one can take anywhere from 6-18 months to occur, depending upon the size of the tank. If your star is starving, transferring to a different tank may provide the necessary nutrition to keep it alive (but we really don't know what blue linkias eat, so it's a hit-or-miss proposition).
Good luck,
Kevin