OMFG! For Mariano Rivera's career to end like THIS would be criminal. I think that the immediate reaction everyone has about "Why is one of the greatest closers of all time shagging fly balls?" is well founded. But Mo has always been a real competitor and an overall great athlete. When he has to cover 1st base, he's there. When there's a tapper up the middle, he's THERE. He has NEVER been a lazy fielder, and that's been one of the unsung portions of his game. He's not just about the cutter.
I think every Yankee fan thought that this might possibly be his final season. He's 42 years old, he's one of the greatest closers in MLB history, and he's sure to be a first ballot Hall of Famer. And I don't think anyone aside from Jamie Moyer wants to be pitching into their mid to late 40's. I think Mo is going to try to make a recovery so that he can leave the game on his own terms, but only after the 2013 season.
As for the circumstances of the injury - how many ball players have gotten hurt because they got tripped up at that joint between the outfield grass and the warning track? I've seen it on numerous occassions.