If Posey was to come back to Boston it'd have to be after he first cleared waivers, then cleared through the bidding process between all the teams under the cap. I expect that with his age and lack of production he'll make it through clean... but do the Celtics actually want him?
Posey isn't the same player he was back in '07. He really only is taking three pointers at this point of his career, and only making between 31-33% of them. Then again there's always the fact that he knows Doc's system, he knows these guys, and once reunited with KG he would push those 35 old legs to their max.