You would certainly hope; and yet, long uptimes unforeseen by designers can have devestating consequences:
> A government investigation revealed that the failed intercept at Dhahran had been caused by a software error in the system's handling of timestamps. The Patriot missile battery at Dhahran had been in operation for 100 hours, by which time the system's internal clock had drifted by one-third of a second. Due to the missile's speed this was equivalent to a miss distance of 600 meters...the Scud impacted on a makeshift barracks in an Al Khobar warehouse, killing 28 soldiers.
> As a stopgap measure, the Israelis had recommended rebooting the system's computers regularly.
There are several types of routine checks, I think Boeing calls them A/B/C/D (with subtypes, depending) Airbus has a different nomenclature but the idea is the same.
