If the engine were running at low rpm's (near idle) and was overheating, it is likely that thermal expansion was enough to tighten bearings, piston ring to wall clearance etc. so that the engine did stop of its own accord. Or if it were running at a higher rpm and suddenly brought to idle speed, it would die of its own accord. This is very normal for an overheating situation. It would not restart until it cooled enough for tolerances to go back to normal. None of this applies to a situation where oil pressure dropped and metal to metal surfaces were not lubricated. Then the engine parts would weld and the engine stop and would never run again. It is for this reason that some engine manufacturers put a kill switch into the oil pressure system since the engine is soon going to die and never recover anyway. But loss of oil pressure is rare and pretty easily detectable if you are careful to test run after oil changes. Oil pump failures almost never occur. Tom Averill