We've had "teeter" closers for the last 5-6 years, and they still seem to save about 40 a season. Mike Williams was the same exact way. Heck, even Mike Fetters saved a bunch of games for us. The point is that the role of a "closer" in Pittsburgh is totally different from the ones that pitch on the top teams. The New Yorks and Bostons of the world use pitchers that can completely dominate three batters by either having a super fast fastball, crazy breaking ball, or wicked change...or all three. The Pirates just use someone they are confident in using at the end of the game. Lots of times they give up walks or a few singles, but at the end of the day, they get all the outs.
No lead is ever safe in Pittsburgh...it's rare to see guys like Gagne, Rivera, or Wagner blowing a game ever. 95% of the time at least one if not two guys get on, but somehow we get the outs 85% of the time.
As far as Mesa goes, I've said it before...If he blows up (especially if we actually start winning games), then he'll be out by the break. If he does well, he either stays because he's cheap or he gets moved for prospects. At that time, Torres or Gonzalez will move up...it's anyone's guess as to who gets the first shot.