Probably depends if the service life is in practical terms limited. Offhand I'd guess it's probably very long. MEMS accelerometers in airbag sensors have to stay within tolerances for the life of a car.
For sensors I can see how you could do that (piezo with a small weight attached) and it will likely live a very long time. But for an MEMS actuator that would be driven to oscillate it would be a lot harder to make that long-lived.
To the extent I can find serivce life specs for MEMS tuning fork gyroscopes, which are driven to oscillate, they say "more than 100,000 hours" - about 10 years of powered-on time, which, for an automotive application like roll-over sensing, is essentially forever, since cars have a low duty cycle.