A friend was hanging a new light fixture (replacing an existing one) and accidentally drilled into the romex behind the wall. He found out because when he flipped the switch, the breaker tripped. He removed the new fixture and the screws holding in the metal box, flipped the switch, and the other two lights on the switch came on just fine.
Question. How concerned should he be about the cut romex that is in the wall? Most likely, the wire is not cut, just had some of the insulation scrapped off. In fact, by his best guess (by measuring the resistance) the screw cut into the black wire and not the white. To get access to the romex would be a real pain.
Any suggestions?