This was basically known.
It comes to down to whether the Sox want to carry him on the 40 man roster over the winter when who knows when he will pitch again. They have done this before to free up roster slots, and it isn't uncommon around baseball. Tyler Johnson is the last one who comes to mind. Typically the try to resign them to a minor league deal because they don't really want them to leave, but they also want the roster slot to protect someone from Rule 5 or something like that. It comes down to is eventual Ryan Burr post surgery worth exposing another player to the draft, or DFAing someone else in the meantime.
They are still responsible for his health care and all of that related to his injury until he signs with some one again.