It will be at least September before he comes back, if he comes back at all. In a roto league, you're probably better off cutting bait and getting someone who can help right now. In a h2h league, those 5 starts might be difference makers come playoff time, so I'd hang onto him.
Morris is apparently likely to come off the DL and start Sunday against the Phillies, so you will then have the DL slot for Oswalt. I wouldn't start Morris his first start back though.