Tough decision, but based on the synopsis of Mike Maroth's health prior to his comeback, I'd say that it's better for him to not create any further injury to his elbow. He's got a pretty good future ahead of him if he can continue the kind of success he had in the first chunk of this season...no use in altering that, even though it's a little disappointing a guy like Mike won't be able to be part of the roster during postseason play.
Here's what Leyland had to say:
Link to Story
Obviously I would not want to be in Leyland's shoes making a decision like that, but he's the skipper and he has gotten the Tigers this far. I would trust his judgement as a player, but I'm sure Maroth was still pretty upset. It's good that he got to celebrate the postseason clinching, I guess.