engine repair on 1999 Audi A6

I inherited this auto and it had overheated and it has been sitting for about 1 year. I am going to take it in and how will we know if it is just the head or if a new engine will be required? I know that they need to test the car but there was oil mixed with the coolant and isn't it just better to replace the engine (probably more expensive of course) than to mess around replacing the head gasket and having problems later or are head gasket jobs usually quite reliable

Asked by for the 1999 Audi A6
I would test the oil cooler before you do anything. We have seen these coolers leak internally