1st- As much as we may assume Pierce and/or KG will retire at seasons end, it is far from guaranteed. If, anything, they might feel as if their last opportunity has been stolen from them, and decide to come back for one more go.
Now, if they do retire at seasons end, the best move would be to just use next year as a rebuilding year. Rondo will likely need the entirety of next season to work his way back into form.
I suspect Green is here to stay, for better or worse. Danny seems to really believe in him. Bass and Terry need to be traded for expirings. Once Pierce and KG come off the books, along with Terry and Bass' jettisoned salary, we could have a decent chunk of cap space and probably a high lottery pick to go along. Summer of 2014 is looking like the year to make our move.