It is Service Station's responsibility, no doubt. However, a lot has to happen before head gasket is blown off. The engine will have difficulty in breathing so much so that it is impossible to be in 3rd/4th gear any more, excessive knocking with jerks & will shut itself off many times before it gets into the danger zone. The smoke will come only when it is cranked started again & pushed for more & more. So here are some queries, Didn't you notice any kind of abdnormal behavior of the engine? It is at Service Station this time but in general, such incidences are not out of question with hypothetical situations like radiator may get leaked due to some underbody hit & drain itself out of coolant when car is parked at rest. You need to elaborate it more, i guess!!! It should be a good learning for all of us & we may suggest you accordingly.