Cleveland will already get two top-40 draft picks for C.C., so they will be looking for more. Now, that more can be two other top-prospects that are more advanced (AA or higher), or more than two less advanced top prospects (high-A or lower), or some combination thereof. The team trading for him will likely want to work out an extension so that they get him for longer than just the 1/2 year rental.
I think this is the wrong thing to do if the Sox are involved. I don't like his conditioning and think it will become more of an issue in future years. Therefore, the calculus becomes should they give up the "more" to go hard after a title this year? Well, let's first consider what the "more" is likely to be.
I figure, in terms of minor league talent as of the start of the season, if it's only two players, they'll likely have to be Jed Lowrie and Justin Masterson / Michael Bowden. Because of Pedroia and Lugo's contract, Lowrie is probably expendable. Losing Masterson or Bowden would hurt, I think. Don't forget, though, they would then be getting the two top-40 picks, and next year's draft class is looking like a deep one. So, the net "loss" is the time it takes to advance prospects drafted in '09 to the level Lowrie and Masterson / Bowden are at now and the risk that they never advance that far. When you look at their most recent drafts and consider how many of their early picks still haven't broken out, that seems like a decent amount of risk. That said, given the state of the roster / farm, I think it's one they can live with.
What if it's more bodies but at lower levels, like say, Anderson, Lin, and Bowden? Lin? A potential future CF - expendable because of Ellsbury (Kalish, Westmoreland - if he signs). Anderson? Best power prospect in the system - his loss would hurt, but he's not that advanced and he could be replaced in the draft (theoretically). Bowden? Probably their best pitching prospect right now despite Masterson's MLB performance, but if they are able to keep Masterson, this doesn't hurt too much at all (given the age of '09 internal rotation options) - toughest to replace because of advanced level of play. These guys are all 1st round talent, but they'd get two more of those in return, so it's a move they can live with.
The big question is, do they need him? The current rotation features Beckett, Lester, Wake, Colon, and Masterson, with Matsuzaka, Buchholz, and Schilling (possibly) ready to step in when needed. He's better than all but Beckett, and that is some serious depth, but I don't think it is their area of weakness. It is not likely to be what prevents them from defending the title. I think the middle-relief issue and the Ortiz issue should figure first and foremost in their transaction manuevering. Don't spend to fix what really isn't broken. Focus on the flaws.