It's not totally out of the realm of possibilites that they can sign them all. They don't have to extend anyone for a couple years. But if say the get Pedroia and Papelbon this season. Maybe Lester and Youk next season. Then the following year Papi comes off the books(replaced by Lars, who will be cheap for awhile). So does Beckett. And the following season Drew comes off the books.
Out of all of them tho, I don't see them letting Pedroia or Lester walk, Papelbon either. Youk on the other hand is almost 30, so in a couple years, they might very well let him hit FA.
I'm sure the FO has a plan going forward to keep the players they want around.