I would have sent him. The way Bumgarner was pitching, that was their only hope. A Pete Rose style slide (plow through) at home plate would have possibly jarred the ball loose from Posey and made for an exciting way to end a rather entertaining world series even if didn't work out IMO.
He would have been out by 30ft with a decent throw. On the flip side what are the chances the fielder throws the ball 10 ft offline from the short outfield where he would have thrown from?? I've seen lots of bad relay throw homes easily offline by that much. Considering the odds of a hit to knock him in were around 20% since batting average against Bumgarner there is about .200. I'd say the relay man make a real bad throw more then 20% of the time. So odds could have favored sending him even if he is out by a mile with a good throw.
Whats more likely , the next guy getting a hit or an errand throw?