Given how much money the Cs have tied up in existing players, plus the money they will likely spend on Jeff Green and probably also Krstic, I don't see there being much of an appetite for paying BBD or, for that matter, working a sign and trade (unless it brings back a Center, in which case Krstic wouldn't be resigned).
For illustration, I imagine that Jeff Green will get a contract starting at around $7M and that Krstic will get one starting around $5M (I'm probably way lowballing this), which is $12M next year on top of the $72M already in salary. That brings salary to $84M before considering rookie salaries and assumes no MLE spent on anyone. Given that, are the Celtics really going to want to sign BBD or work a S&T?