How much will the Giants miss Pagan? The easy answer is "A lot ... unless they don't."
The Giants are 56-35 when Pagan starts (entering Tuesday night's game), meaning they're 29-36 when he doesn't start. So by citing that statistic I just created a story that makes Pagan appear like he's the most valuable player in the league. Twenty-one games over .500 when he starts! Seven games under .500 when he doesn't!
Of course, it's foolish to suggest one player makes that kind of difference, although you hear this kind of stuff all the time when people discuss MVP candidates. Pagan was in the lineup early in the season when the Giants got off to a great start and then again when they turned things around in August and September. That doesn't mean he's the primary reason for those periods of success, however.
I'm not knocking him; Pagan is a good player who hit .300/.342/.389 in his 96 games, giving the Giants solid production from the leadoff spot. Defensively, the metrics are split on him: defensive runs saved says he's slightly below average while total zone rates him above average. Considering he's 32 and played through back issues, my guess is he's probably lost a step out there. The total package adds up 1.5 WAR.
Luckily, the Giants have a capable fourth outfielder in Gregor Blanco. You remember him as the guy who stepped in for the suspended Melky Cabrera two years ago and helped the Giants win the World Series, playing solid defense in left and contributing some timely hits in October. He's hit .260/.337/.378 in 422 plate appearances this season, actually hitting for a little more power than Pagan. Blanco has hit lefties better as well (.283/.333/.375), at least well enough that Bruce Bochy can start him against southpaws. So, based on 2014 numbers, the change from Pagan to Blanco isn't much of a decline, if any.
But the other problem for Bochy is left fielder Mike Morse is currently out with an oblique injury, which has sidelined him for the Dodgers series. The Giants are hopeful he can play this weekend against the Padres, but that's no guarantee and he'd have to shake off the rust as he's batted just twice in September.
The Giants' fourth outfielder at the moment would be Juan Perez, a defensive guy who is hitting .167 in 99 PAs. The other option is Chris Dominguez, a 27-year-old minor league vet who played the past two games. He hit .274/.307/.460 at Triple-A Fresno with 21 home runs but 143 strikeouts and just 22 walks. So if Morse isn't ready by the postseason, the Giants appear to have an obvious hole in the lineup.