Seen many engines have oil/coolant mix & run a long time. My mother's Omni lost the head gasket with ~120K on it & was driven ~10 miles with a gallon of coolant in the oil. New head gasket & water pump, coolant flush, fresh oil...the car ran another 178,000 miles.
Saw someone drive a truck ~50 miles with the oil mixed about 50/50 with gas (fuel pump diaphragm failed, driver noticed nothing amiss until the OIL light came on)...the vehicle (old Dodge truck, 318 2bbl) was still running when scrapped 100,000+ miles later due to rust.
