Here's another way to look at that question: What can Freddy Sanchez give the Giants that Matt Downs isn't giving them right now?
While I was sleeping last night, Downs gave them a huge two-run double in the 12th inning. He has given them a .269 / .342 / .403 line, which could be higher with a bit more luck. He's been hitting the ball hard and right at people. On defense, he's given them above-average glovework according to UZR, though beware of the small sample size.
Is it enough to keep him on the roster when Sanchez returns? If the Giants want flexibility, they'll keep Ryan Rohlinger, who can play shortstop in a pinch. Or they can keep Eugenio Velez and his toolbelt of sub-mediocrity. He can make things go clank in the outfield and second base! He's fast, so he can make fast outs and get caught fast stealing!
Unfortunately, a backup infielder who only plays one position doesn't make sense on this roster. Well, except for, um, the backup first baseman who doesn't get spot-starts and doesn't come in for late-inning defense. Travis Ishikawa: Irreplaceable Clubhouse Presence. Order your DVD now.
My guess is Downs will head back to Fresno with a big pat on the back. When he arrives, he should find an outfielder's glove in his locker, because a little time in LF wouldn't hurt his chances to rejoin the big club ASAP.
The dirty Sanchez secret, which isn't much of a secret, is that Freddy's career line of .299 / .334 / .417 isn't much better than what Downs is doing now. And his career UZR at second base is just slightly above average. His backers will point out that he's capable of great things such as batting titles when he's healthy. I'll let that one sit there on a tee for a few moments.
I'm not saying Downs should give F-Sanch the Wally Pipp treatment, but he has worked himself from fringey prospecthood into useful player with an outside chance of big league starter. Unfortunately the size of that chance as a Giant is inversely proportional to the size of Sanchez's contract and veteran warriorhood. Even if Freddy struggles for the next month, Bochy will keep running him out there to help him find his sea legs or bearings or timing or something. The only way Downs becomes a starter again this year is if Freddy returns to the DL, which is an ungentlemanly thing to wish for.
I'd love to see Downs stay, but I'd also hate to see him rot on the bench with three pinch-hits and one start per week. Downs is already 26, but what he's done the past few weeks makes me wonder if he'll find his groove in his late 20s. Not quite like this guy did, but enough to make him a viable alternative to a low-OBP, low-slugging second baseman who can't stay healthy.