Does the exhaust steam when it's warmed up? Does the engine oil have a chocolate milk shake appearance? How about the radiator - is the coolant the correct color or milky? There are kits to test the antifreeze to see if the head gasket is leaking combustion gases. If your shop doesn't or can't figure out where the leak is, find a different shop.
If the headgasket is leaking, I'd get it fixed rather than "waiting" for the whole thing to let go.
