The consistent story line surrounding the Yankees so far this season has been that the team needs to tread water until the injured superstars, Mark Teixeira, Curtis Granderson and Derek Jeter, can return. Last week we found out that Jeter has suffered a set back and won't be able to play until July. Without question, this harms the team. Much has been made of Jeter's recent decline, specifically his sub-par 2010 and 2011 seasons, but even that weakened Jeter gave the Yankees above average offense at shortstop. Furthermore, Derek bounced back in 2012. The .347 wOBA Jeter posted in 2012 was far from his .365 career average, or the production he's put up in his signature seasons, such as 2009, but it was a welcomed return to form, and evidence that maybe Derek had one more .340 plus wOBA season in him. As frustrating as it is to watch the Yankees play Mariano Rivera's final season without Jeter in the lineup every day, Derek will come back. He's still under contract and too competitive an athlete to go out this way. The real question is therefore how much damage his extended absence will wreak on the team. Given that Derek will miss half the season, we can measure the production this will cost the Yankees as a whole.
According to Fangraphs, Derek has averaged just under 2.6 fWAR over the past three seasons (Baseball Reference puts the figure at 2.3 bWAR). Taking that as a baseline, its safe to suggest that over the course of half a season, even an aging Derek Jeter will be responsible for between one and two victories for the Yankees. It may not sound like much, but that's a hefty contribution.
Unfortunately, Jeter's contribution isn't zero sum. The Yankees have to put nine players on the field. Less Derek Jeter usually means more of Eduardo Nunez or Jayson Nix. Nunez is off to a terrible start. Fangraphs suggests he's been a net negative on the team, with an fWAR of -0.2. Last season he managed only 0.5 fWAR in limited playing time, which means at best Nunez is a slightly above replacement level player. Jayson Nix isn't any better. He clocks in at -0.2 fWAR on the season already, and managed 0.3 over all of 2012.
Taking it all together, assuming Nix and Nunez actually cost the Yankees games, Jeter's absence over the first half of the season will probably take two games off the Yankees win total during that time. That may not sound like much, but the AL East will be tight all season long and there is no guarantee that both Wild Card teams will come from the AL East when Texas, Oakland and Anaheim all have post season plans in the AL West. Jeter's absence will most certainly be felt.