sounds kinda weird to me. The car should not just all of a sudden start running rough as soon as the oil light comes on. Make sure they didnt accidentaly fill it up with diesel fuel or something. I have seen it done before. If the oil level is ok, crank the car up and listen for the top end to see if its chattering really bad. Listen to the bottom end for knocks. If you dont hear any weird noises and everything sounds ok then more than likely it may be just a bad oil pressure switch, oil pressure still needs to be verified by removing the EOP switch and screwing in a gauge. If you verify good oil pressure(10psi for every 1k rpm) and dont hear noises then you can safely let the car run and check for other issues. They may of had a coil pack go bad. Never know.