I am all for bring dunn back in 2014, or more accurately I am against paying him $15 million to just to sit at home. I wouldn't let him off the hook.
Since the baseball culture typically doesn't ask players like the NFL to renegotiate their contracts due to poor performance, I don't expect the Sox to ask that of Dunn. Nor do I expect Dunn to be altrustic like Ted Williams who gave back 33% of salary for his perceived poor performance one year.
Given these realities, I would demand of Dunn to work his tail off the offseason. Hopefully Dunn has enough pride in himself to do this. This is his last chance under this contract. If 2014 proves the Sox aren't contenders, I would expect Dunn to play nearly every day or at least platoon.
It's a long shot, but maybe some contenting team may be desperate enough to grab Dunn if/when he's in a hot streak.
But if you just eat his contract, there's no chance of that. Just letting him go home with $15 million is like a golden parachute. Who wants that?
If they are contenders, it's a different story, he will probably hurt the team. I assume he can't be sent to the minors, but if so, he has the right to refuse it??