The F-117 has been in service since the early 80s, so this is a reasonably decent shelf life for that platform. Remember that this thing is less a "fighter" jet and more a strategic bomber, since its air-to-air capabilities are negligible.
The F-117 was made redundant when the F-22 Raptor came on line in 2005. The F-22 is superior in speed, stealth technology, armament and bomb payload. It is a true air superiority fighter, and has the cajones to mix it up with the world's best fighter aircraft. It's stealth capabilities give it a distinct advantage in air combat missions, as well as in strategic bombing missions and general avoidance situations.
The Raptor is the world standard in fighter technology at this time. We don't need the F-117 anymore.