I happen to own a coach that absolutely requires that the airsprings in the rear suspension are functional. That is all it has and if one goes out (on my coach's vintage) it cannot be moved.
The real answer to your question is very dependent on the model and manufacture of the specific part. The OE for the coach had a life of about 20 years. The newer replacements seem to only last about 15 years. I personally would have to go with current manufacturing processes and vote that like tires, start worrying at 10 years.
Matt