If Ref were DFA'd, the Sox would either have to trade him, release him or place him on waivers, I doubt they could trade him and given the contract extension, they aren't going to release him.
That leaves waivers; i don't know if he would clear them. He might have some value to a contender as a bench guy, so it would not be a for sure thing that he would clear waivers. If he did, the Sox could then outright him to the minors. However, since he has more than 3 years service time AND has been outrighted before in his career (I think by both Cleveland and the Twins), he could refuse the assignment and become a free agent.
I don't it happening. For one thing, he is a cheap bench guy who knows and is seemingly content with his role. He's a righty, which the Sox are sorely lacking.
I see Tapia as a more likely candidate for release or Duran sent down.