As mention assuming neither the sender and guage have failed. Could be the oil pump chain has failed! You haven't mention any more leaked oil, a close inspection of the forward area of the oil pan might reveal a cracked or damage pan where the chain piled up.

A vacuum pump failure usually has the bearing coming apart with parts dropping down into the timing chain chase where a hard part gets between a chain and its sprocket. Maybe a ball bearing got between the oil pump drive chain and sprocket.

Running the engine at all is ill advised now, the cam will eat up the head in short order without pressurized oil. There are no replaceable bearings, only a rebore and new oversized cam if your lucky!