There's no way I'd scrap the whole bumper for that little piece. It should be easy to reconnect to the bumper. It was probably only glued or heat welded on at the factory anyway. Give it a try with epoxy adhesive, but not the five minute variety. Remove the screw holding it to the inner guard lining, clean it up and cement it in place and leave it for 24 hours before trying to re-attached the inner guard.