No Major League Baseball team, let alone the Yankees, will probably ever have such a historic, high-achieving group of homegrown players on their roster for such a long stretch of time as the "Fab Five." Bernie Williams, Jorge Posada, Andy Pettitte, Mariano Rivera, and Derek Jeter were the backbone of the recent Yankees dynasty and were responsible for a combined 272.1 WAR (!) over their careers with the team.
Replacing the talents of such key contributors would be a challenge for any team, let alone a team with such constant media coverage as the Yankees. There's also the pressure on the the players stepping into the shoes of the Yankee legends, all of whom were subjected to extreme scrutiny from day one on the job.
However, despite the pressure, all of the "Fab Five" successors almost seamlessly inherited their positions from the greats, and at the very least did not represent dramatic losses in production from their predecessors' final seasons.
Of the "Fab Five," Williams was the first to step away from baseball (his career also began before the others'), doing so following the 2006 season. In his final season with the Yankees, Williams hit .281/.332/.436 with 12 homers and an OPS+ of 96. Rather than replace Williams through a free-agent signing or trade, the Yankees opted to replace him from within, giving the job to Melky Cabrera.
Although free agent Johnny Damon saw most of the time in center in 2006, Cabrera often played left field opposite Bernie in right after Hideki Matsui went down with a wrist injury, and he hit .280/.360/.391 in 130 games. While he did not hit as well as he did in 2006, he still managed to hit .273/.327/.391 in 150 games with an OPS+ of 88--not great, but not terrible. Joe Torre also recognized Cabrera's defensive acumen in center, trusting him with Bernie's old position in 2007 over the aging Damon.
Cabrera saw his production slip in 2008, but his 2009 improvements were a major part of the team going on to win the World Series. In his three full seasons with the team in center field, he batted .267/.323/.385 with 64 doubles, 29 homers, and 3.2 WAR. Melky was nothing special, but his consistency and occasional bursts of offensive potential made him a fan favorite and decent, cheap replacement for Williams.
Posada was the next of the "Fab Five" to retire. He played poorly in 2011, his last year in pinstripes, hitting .235/.315/.398 with an OPS+ of 90. He primarily served as the team's designated hitter after losing the starting catcher job to his successor, Russell Martin, who hit .237/.324/.408 with an OPS+ of 95. Martin continued to catch for the Yankees in 2012, hitting .211/.311/.403 with an OPS+ of 91. Again, not incredible, but serviceable for a player in a demanding position. He was definitely not worse than 2011 Posada, so it's somewhat fair to say that he adequately replaced a member of the storied "Fab Five."
None of the remaining active "Fab Five" members signed off in 2012, but the conclusion of the 2013 season saw the departure of both Rivera and Pettitte (the second time). Rivera's last appearance in pinstripes occurred first, two days before Pettitte's.
After being a constant presence as the Yankees' closer for more than 18 years, Rivera retired at the age of 43. However, history repeated itself as Rivera's setup man, David Robertson, assumed the role of closer the following season just as Rivera once did after the departure of John Wetteland. In his last year with the Yankees, Rivera pitched to a 2.11 ERA (3.05 FIP) in 64 innings and had 44 saves. In 2014, Robertson pitched to a 3.08 ERA (2.52 FIP) in 64.1 innings with 39 saves, somehow smoothly replacing the greatest closer of all time.
Pettitte also retired following the 2013 season, during which he pitched to a 3.74 ERA (3.70 FIP) in 185.1 innings. Other than relying more heavily on in-house options such as David Phelps and Shane Greene, the Yankees sought to replace Pettitte's production by signing Japanese star Masahiro Tanaka. The team signed him to a seven-year, $155 million contract with an opt-out clause following the 2017 season. In 2014, Tanaka pitched like the ace he was expected to be, performing to a 2.77 ERA (3.04 FIP) in 136.1 innings.
The only bump in the road came when Tanaka was diagnosed with a partially torn UCL in the summer. After rest and rehab, Tanaka came back strong in 2015. He pitched to a 3.51 ERA (3.98 FIP) in 154.0 innings, and missed fewer games due to injury, though the injury bug did still bite. The Yankees (and fans) have high hopes that Tanaka will fully return to ace status in 2016 and be the anchor that the rotation desperately needs.
Jeter was the last of the "Fab Five" to hang up his cleats. Though always a valuable veteran presence, by the end of his career he dramatically slowed down; in his final season, he hit .256/.304/.313 with an OPS+ of 76. It would not be hard to replace this performance, but whoever the Yankees brought in to play shortstop would still be subjected to endless scrutiny because, well, no one would be Jeter.
Fans were divided after Cashman traded the surprise success-story Greene for former top prospect Didi Gregorius. However, after the first few weeks of the season, fans were suddenly united in their dissatisfaction with Gregorius. What a difference a full season makes. While it is still early, the Yankees currently look like the winners of the trade, as Gregorius slashed .265/.318/.370 with an OPS+ of 91 and stellar defense. He also endeared fans with his personality, most notably through Twitter. If all goes as planned, Gregorius will be standing at shortstop for at least the next few years to come.
Overall, there was just no way the Yankees could perfectly replace all five members of the aptly named "Fab Five." Considering just how good that group was though, it is truly amazing just how well the Yankees have done given such a daunting task.