In a truly bizarre scenario, if the Sox are without some combo of Bradley, Mookie and JD Martinez, it is entirely possible Rusney Castillo makes the MLB club next season. The Sox are paying him anyway, and the only real savings is on the luxury tax. If they are under the limit and there is no tax to pay, there is that much less of a reason to keep him in Pawtucket Purgatory. (I know it will be Worcester Purgatory next year, but I like alliteration.)
Of course, there is always the very real chance that he just flat out sucks, which would be a very real reason to keep him in AAA...