I agree with the last few comments. Keeping Sale is not without risk. (Trading also has risk, but it is spread out over several players.)
Another aspect of the rumor is the inclusion of Rios. There was a posting on mlbtraderumers.com earlier today that the Sox were disappointed with the offers for Rios so far. Now, these are all rumors, and we don't know what is really going on. However, bundling Sale with one of the experienced, older, and more expensive players like Rios may make it easier for another team to trade the "crown jewels" of its farm system and take on the added salary expense.