I am trying to think of a scenario where bringing him back makes sense. If Hahn offers him a good contract and says he would be the starting catcher with Grandal moving to more of a DH/1B role then I think we keep him. Unfortunately that would require Grandal to go along with it and I doubt he does.
I then questioned where Vaughn would play in that scenario. He wouldn't. Abreu has the next two years and will most likely be extended after that. With Grandal moving into that 1B/DH/backup catcher role then Vaughn has no place on this team.
I love McCann, but I feel Vaughn's bat is going to be incredible and I would hate to trade him or see him get the Collins' treatment, not that the two should ever be compared.