A few things that people brought up in the comments.
First, should a lefty have been used versus Sandoval? I didn't even think about this at the time but it's an honest question. He's much worse from the right side. The immediate "Why don't you use Blevins" call is wrong. Once you turn him around and he gets to face Blevins as a righty - that's the one thing I've said needs to be avoided at all costs. Righties hit .298 / .398 / .423 this year, but what about Thornton?
Sandoval vs Lefites .199 / .244 / .319
Thorton vs Righties : .236 / .306 / .327
Sandoval vs Righties : .317 / .363 / .461
Storen vs Lefties : .253 / 274 / .319
I think Thornton would have been the right call here in a perfect win-maximing world. Why wasn't it considered? I think two reasons. One is Storen is the closer, he faces lefties all the time, will have to get out lefties, blah blah blah. The other reason is that Posey crushed the first pitch. There wasn't extra time to think of that next move. Sure you should be thinking 2-3 moves ahead but you don't always especially when you are agonizing over the current decision.
This wasn't egregious, but it's there.
Second, you're right that "we're going to bring in our closer if one man gets on" is not a great line of thinking. It happened to match up to reality this night. ZNN had reached 100 pitches, looked winded vs Panik, and MVPosey was up. But what if he guy gets on because of a bloop hit, swigning bunt, or booted routine ball? It has to be case by case. I'm not exactly sure that they are super by-the-book about it though. The quote can be read with an implied "in this game" sense. Zimmermann was losing it therefore... type of thing. That's the hope anyway.
Third, the idea that SF was glad to see Zimm walk. There is truth here. If you feel you can't beat a guy it gets in your head. Until it doesn't. It's like going with the hot hitter. He's hot... until he isn't and you have no idea when that switch is going to be pulled. If you want to make decisions like that it's fine, but understand you are basically guessing, and game in and game out that's not a good way to manage. Also understand at that point it doesn't really matter how the Giants felt, it matters how Posey felt. The Posey as I noted, who hadn't missed a pitch ZNN had thrown all night and had lined out hard last at bat. I think he had a pretty good read on ZNN and wasn't jumping for joy when the guy was pulled. That's my guess.
What now? WIN goddammit. Win.
Do you put Zimm in? The optimal line-up is probably something like Espy at 2nd, Zimm in LF and Span and Cabrera sitting. That's unlikely. If its just Zimm, for LaRoche, makes the most sense (best position for Zimm worst hitter vs LHP. LF is most likely, as Bryce like everyone, isn't hitting, and is not a veteran. As others have noted - with Fister on the mound you can probably get away with a worse OF defense (sitting Span who doesn't hit lefties well himself and lacks any indication that he might see Bumgarner ok which you can get from LaRoche's history if you don't mind small sample size judgments) but I can't see MW sitting his lead-off hitter and best OF defender. Especially given how apparently Lorenzo Cain has single-glovedly lead the Royals to the ALCS.
Fister should be there but Roark and/or Gio should be ready at the drop of a hat. And frankly I wouldn't mind seeing Strasburg up. I don't want to see any pitcher saved for tomorrow because there might not be one. Use the best bullets in your gun tonight early and often. Right now worry about winning the game, not the series.