Don't hope for a leak. Chances are the pressure switch or it's associated wiring has been disturbed or damaged. The oil pressure switch is on the front of the engine, directly above the oil filter. Make sure the wiring has not been unplugged by accident. Personally I would not drive the car until wiring has been checked and, if okay, pressure switch has been changed. A new pressure switch is only about a fiver and easily changed by any DIY mechanic. I would suggest you don't use the one you used last time! He sounds a right numpty.