Well replacement might be a tough word, because no one is going to ever replace the supreme production supplied by Mariano Rivera.
Replacing someone was as great as Rivera in their own line of work is the ultimate no-win situation. It rarely works out the same way, and no one usually remembers the replacements.
Quick: Who replaced Lou Gehrig at first base? Who replaced John Wooden at UCLA?
Mariano is the greatest closer of all time. Not the greatest relief pitcher (that would be Rollie Fingers because of his multiple inning durability), but Mo is the one pitcher you want on the mound for three ninth inning outs holding a one run lead.
Finding a new closer is going to be a difficult challenge as no one knows how long Rivera will continue to want to pitch.
At age 40, Rivera has shown no signs of vulnerability. He still sports one of the best closer ERAs with 1.05 and 20 saves, and a WHIP of 0.641. He also retired an incredible 24 straight batters in the month of June.
Still highly effective, how long will Rivera want to pitch? Similar to Derek Jeter and Andy Pettitte, the Yankees will allow Rivera to make up his own mind when he wants to leave the game.
Rivera has mentioned that signing a series of one-year deals (similar to what Pettitte has done) would be acceptable to him.
I believe Rivera will pitch at least two more seasons after 2010. The "Core Four" will begin to gradually leave the team after this season (Pettitte retiring) and after 2011 (Jorge Posada not being re-signed).
If I were Mo, I would not want to retire the same season as another long time Yankee does.
I believe Rivera will then leave after the 2012 season, which makes getting my preferred replacement very difficult, as that guy is available sooner than the 2013 season.
Here are the five top candidates for the eventual new Yankees closer spot, and Joba Chamberlain is NOT on the list.