I have no idea what is more or less likely. Not enough information. I'm just confident that the Yankees will be better off with a good defensive 3B who can play all the time. Headley fits the bill. Prado does too, but I like his bat better at 2B. I would also hate to count on Refsnyder being productive for a full season. Counting on ARod to contribute fulltime at any level of competence, especially defensively, is risky. Better to re-sign Headley and tell him 3B is his. Worry about ABs for ARod later. If ARod hits so well that you need to keep him in the lineup, then that is a problem I'm sure the Yankees would be happy to deal will. Plug him into the DH slot and sit guys like McCann or Beltran when they need a rest.
Guys will get injured off and on throughout the season. Finding ABs, whether at DH or another position, probably won't be an issue. Counting on someone to play a position defensively that they can't manage well anymore might be a problem, and one I'd like to not see for a change.