He's the best thing the Red Sox have in terms of a #5 SP right now. Having said that, if the Sox go out and sign Oswalt, you put Bard back in the bullpen. Oswalt will be ready to throw sometime in June from what I've heard, so I said Through June. Even if Oswalt isn't signed by the Sox, you go to DiceK.
Bard's innings limit should be about 130-140 IP this year. That's doubling his innings from last year. Another 5 starts will put him right around 75 IP. Then you throw him in the bullpen the rest of the year. Even if you want to stick with him as a SP next season, you still cap his innings. And it's not a cap on SP innings, it's a cap on total innings. You don't just scrap the guy in early August when he's reached 135 IP. You put him into the bullpen where he can come out for 40-45 games out of the pen as well.
By the way, he's lost a lot of velocity and seems to be throwing on the side of the ball rather than on top of the ball. That's worrisome. Gets a bit more movement, but he's a flamethrower, not a Greg Maddux.