He probably would have left Lidge in there had it been a righty coming up. I think the point was that he shouldn't have been at the point of facing Griffey, who was the 4th batter in that inning. Had he gotten one of the two that reached base, Garner might have left him in as well since a Griffey homer wouldn't have hurt.

It was a bit shocking and took some serious balls, but it worked out great in the end. As barzilla said, at this point in the season, only victories matter.