Ming
There is no situation in which an airliner will be shot down before an interception. Any such problems ocurring over any NATO nation are dealt with in a uniform manner. The Air Policing organisation (of which I am part) has a very strict code of conduct and we practice on a regular basis. Not only do we police our own soverign airspace but we have continuous contact with our NATO allies 24/7.
Listening to certain frequencies can be difficult due to equipment and geography and so, in the UK, we liaise very closely indeed with our ATC organisations.