Too bad we don't have Carlos Silva anymore. I don't blame the Cubs for releasing him in light of his temper tantrum. Silva should have been taking what he could get. His stint in the minors would have been very brief.
I expect we'll see Thomas Diamond make the next start needed by a 4th starter. We might see a reliever for a few days until that start is needed though. A couple years ago this would have been Sean Marshall making a spot start, but now that he's dominant in the bullpen he'll probably stay.
The other guys on the radar will be Casey Coleman and Jay Jackson. I guess I'd pick Jay Jackson. William Trey Mcnutt is another possibility. I'd avoid this and let him continue his developement though.
It seems a bit hasty to put Wells on the 15 day dl, I expect he could have came back sooner. Cashner being a starter for the first time would probably have his innings limited anyway so it doesn't matter if that's now or later.