Every team starts the season thinking, "we're world-beaters if only youngsters A & B develop like we hope, injured-last-year folks C & D stay healthy, and aging vets E & F return to form!" But life doesn't work that way. If possibilities A-F all are coin tosses, you never flip six straight "heads" -- or, at least, the odds are only 1 in 64 of doing so, in which case, congrats, you're the 2014 Royals. So it's unrealistic to muse, "how great will we be if everyone stays healthy and plays to max potential?" The more realistic and interesting question is, "what if the most likely problems happen?" What if youngster A (Didi Gregorious?) doesn't develop, injured guy B (Carlos Beltran) doesn't recover, or aging vets C-F (Mark Teixeira, Brian McCann, Stephen Drew, Alex Rodriguez) don't bounce back? With pitching, the answer is obvious: losing a #1-2 starter means you're screwed to the tune of 3-5 wins each; you're replacing a good-to-great pitcher with someone too scrubby to be one of your top five starters – Esmil Rogers replacing Masahiro Tanaka or Michael Pineda. With position players, it's less obvious what "disaster scenarios" matter most. It's not just who's best or brittlest; it depends on player quality (Brendan Ryan's brittleness doesn’t cost much), likelihood of long-term injury (a short DL stay hurts little), quality of contingency plan (remember 2014 1B backups Kelly Johnson & Ryan?), etc.
You can find question marks all over the Yankee lineup, but here's my take on how worrisome each position-player disaster scenario is -- starting with the least worrisome.
Worst-case scenario #7: McCann isn't any better than in 2014. Contingency plan: None; John Ryan Murphy won't take his job. Prognosis: Not worrisome. McCann's inaugural Bronx season was disappointing, but after a strong finish, he ended up a nearly league-average hitter and far-above-par defender at both the blocking-and-throwing dWAR tracks and the pitch-framing it doesn't. And Murphy should exceed typical #2 catcher quality. So even just a repeat of McCann's 2014 leaves the Yankees well-above-par at catcher – so McCann isn't one of my top worries.
Worst-case scenario #6: Teixeira loses significant time to injury, surprising nobody other than the guy admirably optimistic about his own brittle wrist, muscles, etc. Contingency plan: Garrett Jones and A-Rod platoon at 1B. Prognosis: Little loss. This is where A-Rod's possible 1B competence matters: it's not that he's valuable as a third-string 1B; it's that he's valuable in combining with Jones into a second-string 1B platoon that could easily match the league-average hitting you expect from Teixeira. While Jones/A-Rod could be poor defensively, Teixeira is 35 and has been a relatively consistently negative-dWAR defender since joining the Yankees. Sadly, Teixeira is mediocre enough, and the backup option solid enough, that an unsurprising Teixeira injury wouldn't be the high-stakes loss it once was. The main modest loss here is that more Jones/A-Rod 1B playing time means stretching Young, Jones, and a possibly delicate A-Rod into more DH at-bats, but that's a modest hit because the added at-bats will be scattered; it's not like Young needs to become an everyday DH.
Worst-case scenario #5: Didi Gregorious's hitting stagnates at the 80-90 OPS+ level. Contingency plan: None; it's his job. Prognosis: Little loss. With his plus defense, that middling offense still leaves him the 1-1.5 WAR he logged in each of 2013-14. That not only exceeds the Yankees' 2013-14 production from SS, but actually is about what Jeter averaged his last five years. So a lack of growth by Didi might crush the dreams of those crushing on Didi, but his presence still would improve the team, as planned.
Worst-case scenario #4: Chase Headley, Jacoby Ellsbury, or Brett Gardner misses lots of time. Contingency plan: Weak backups. Prognosis: Real loss – but low odds. Each is a 3-5 WAR player, and injury isn't that unlikely for any early-30s player playing the sort of quality defense that has them diving a lot. But Gardner isn't especially brittle, and the injury fears you hear about Headley and Ellsbury are overblown. Headley has averaged about 145 games a year; Ellsbury lost lots of time in two years with freak injuries (2010 & 2012), but he's otherwise played 134-158 games a year from 2008-14. I could see any of the three missing some games after a rough dive, or Gardner/Ellsbury tweaking a hammy while stealing – but missing 15-20 games for one DL stint isn't enough to make a real dent in the team's season; replacing a 4-WAR player with someone replacement-level for 20 games costs the team only half a win.
Worst-case scenario #3: Drew still sucks, just like in two of the last three years. Contingency plan: Rob Refsnyder gets the call. Prognosis: Could cost 1-2 wins in a half-season, but little loss after. Refsnyder already projects to hit better than Drew; defensively, spring training showed Ref has rough edges – which is different from "bad" or "untalented." I didn't see much of spring, but reportedly he made some excellent plays while botching some easy ones. As Ref himself noted, he's played barely 200 games at 2B, a ton less than folks getting drafted as middle infielders, then playing several middle-IF years in the minors. And there's evidence he's learning and improving quickly; stats indicate he was better defensively in late 2014 (at AAA) than early 2014 (at AA). If Drew hits like 2014 or 2012, Ref can outperform him with just baseline-competent fielding; a rough-around-edges mix of strong range and error-proneness could easily be enough for his above-par-for-2B bat to make him an improvement. The problem is the Brian Roberts precedent: they could let Drew suck for 80+ games, and the difference between Ref (possibly an average player already) and a sub-replacement Drew could be 1-2 games in a half-season.
Worst-case scenario #2: Beltran still sucks, due to age or ongoing injury. Contingency plan: None; he'll just hurt the team. Prognosis: A 3-win gap between the high- & low-value scenarios. The hopeful scenario is returning to the 3-WAR hitter he was in 2012-13, but in RF he's so statuesque (in the bad way) that he's been a -1.5-WAR fielder for two years running, so his best-case is 1.5-2 WAR – not worth $15m, but enough not to hurt the team. Yet he could be much worse: absent a vita-rays treatment from A-Rod, it's hard to bank on a return to elite hitting from a 38 year-old, especially one who has to play the field most days, who's coming off a bad season, with a recent bad elbow and a history of brittleness (he's averaged just 115-120 games a year for the past 5-6 years). If he's an average or (like last year) replacement-level hitter, he's a replacement-level or much worse player. Yet there's no good contingency plan. Given his salary and the wishful thinking about any decaying superstar, they won't bench him; he'll just hurt any hopes of making it to the mid-80s wins the postseason requires. The backups offer little hope of better: as an OF, Jones offers the same replacement-level-Beltran scenario (near-average hitting, awful fielding); Chris Young offers the same low value overall, just a different mix (average fielding plus replacement-level hitting). The difference between 2-WAR and -1-WAR Beltran is probably the second-biggest variable among position players.
Worst-case scenario #1: A-Rod is done, due to age, lost time, or post-steroid face-melting syndrome. Contingency plan: Replacement-level DH at-bats. Prognosis: A 4-win gap between the high- & low-value scenarios. This is just a more extreme version of the Beltran situation: at their age, and after a lost 2014 for each, there's just such a wide range of possible outcomes. I could see A-Rod bring 3-WAR hitter with (a) more off-days than a non-40something but (b) modest added value as a better hitter than the average second-string 3B/1B. I just as easily could see A-Rod being finished, a negative-WAR scrub. The delta on A-Rod could be 4 wins; he could be anywhere from -1 to 3 WAR – the widest gap in plausible outcomes for any position player.
Which is to say: it's still all about A-Rod. Or, at least, the lineup's biggest X factors are A-Rod, Beltran, and Drew: the difference easily could be 8-9 wins between those three firing on all cylinders or stinking up the Bronx. Sure, other disasters could cost them 8-9 or more wins: Ellsbury and Headley could rupture a hamstring and a disk; McCann could decline further; Gardner could get hit by a bus. But if you're handicapping the most likely disaster scenarios, watch that trio of guys who looked washed-up in 2014 but could well return to being average or better: A-Rod, Beltran, and Drew.