The short answer is 'until something does break'.
I'm not meaning to be a smartass with that comment, but nobody can predict the service life of any machine. There are just too many variables.
There are steps you can take, like preventive maintenance and operation within the design parameters that will extend the service life.
Minor problems need to be addressed before they become big problems, clean fresh lube on wear points, conservative loads, and closing with a 'snap' and not a 'TWANG' and the gun will likely outlast you.
Fortunately, we have craftsmen who can fix and repair just about anything so rather than fret just shoot the thing and enjoy it.
