There are no details on the signing yet, which comes on the back of the apparent dissolution of the Ryan Madson deal. If this one does end up going through, you can reasonably assume that the four years and $44 million that Madson had agreed to is the absolute floor.
UPDATE: Multiple beats saying it's four years, $50 million. Marc put it pretty eloquently on Twitter, I think.
For the Red Sox, it represents the end of an era. In the six full seasons Papelbon has spent in Boston, he established himself as one, if not the best reliever in the team's history, well eclipsing Bob Stanley's record of 132 saves with his 217.
Papelbon's departure is far from surprising. The closer has always let it be known from the very beginning that he was in it for the money, and now he's found his payday. And that's fine. We didn't celebrate him as a classic Sox hero aside from 2007, when he closed the World Series out and river danced his way to celebrity. But he did right by the Sox aside from 2010, and that's not something to be ignored.
Without Papelbon, the Sox will need some help in the bullpen, to be sure, but they can likely find a reasonable replacement and at a cheaper price. So long as they do that--be it with a now deflated Ryan Madson or someone else--the Sox can live without their record-holding closer.