This AP article brings up the possibility of Johnson pitching on short rest, which Brenly rejects:

After losing the first two games of their best-of-five series with World Series co-MVPs Randy Johnson and Curt Schilling pitching, the Diamondbacks send out Miguel Batista to start Game 3 against the St. Louis Cardinals on Saturday night.
“We’re not stupid, we understand what we’re up against,” manager Bob Brenly said Friday. “But we also understand there’s nothing more you can do than give your best effort.”
Brenly said he didn’t consider using Johnson, who was shelled in Game 1, on three days’ rest in Game 3. He expressed confidence in Batista, 8-9 with a 4.26 ERA in the regular season.
“Our feeling over the last couple of years is that Randy is much more effective when he’s able to maintain his regular routine,” Brenly said. “We also feel Curt Schilling is the guy who is best-suited to handle short rest if we do need to bring somebody back to pitch a potential Game 5.

I have to agree with Brenly here. No matter what, you’re going to have to pitch Batista in one of the games, so you may as well do it now, and have Johnson and Schilling strong for games 4 and 5 if you win.