All microswitches have a lifespan that is given by the manufacturer. That doesn't necessarily mean it will magically fail once that limit has been hit, but the manufacturer can't guarantee that the amount of force required per contact will remain the same at that point, or that the switch won't stick occasionally or any of a decent number of issues that affect microswitches crop up.
That said, it doesn't mean a device is unusable, just that it may not perform the same as it did when it was new or within its normal usage expectations.