To be completely honest, I think that ship has sailed and if I am the Celtics head office I really have no interest in bringing Sully back.
This scenario is eerily similar to the Big Baby one. Nice player who was able to contribute in a few ways, had a few big games, then wanted too much money and ultimately got told "cya later". Then went off and ate himself out of the league.
Sully definitely has some skill, but right now he seems to be barely holding his starting job. He started the season strong - now he's back to shooting 44%, he's still taking too many jumpers (never gets tot he line) and he's still struggling to score at a high rate. Conditioning still looks to be no better than it ever has been. The guy is in a contract year - if that's (plus all the competition in Boston's frontcourt) is not enough to light a spark under his backside then nothing ever will.
It's sad to say for a guy who had/has so much potential, but come free agency I must say "good riddance, Mr Sully"