One important thing to keep in mind is that Pierce has value two ways; 1) he is still a viable top-7 or so (you could even argue top-4 or 5) SF, and 2) He is a valuable financial piece, because you can trade roughly 18.75 million in salary back to the Celtics, but you'll only take a 4 million dollar cap hit if you waive Pierce before 6/30.
Dallas doesn't has some ammo to offer for Pierce, and it would behoove them to acquire him, especially if they included Vince Carter in the deal. They could trade literally their entire roster, besides Dirk (Marion/Carter/Cunningham/James), and they could include the player selected with their #13 first round pick as well (they cannot trade the pick outright because they have other trade obligations on it, and only get to keep it this season through a top-20 protection).
So Dallas Trades: Marion (9.3), Carter (3.2), Jared Cunningham (1.2), Bernard James (.78), Jae Crowder (.78), #13 overall (roughly 1.6 million cap hold)= 16.8 million
Boston Trades: Paul Pierce ($15.3)
So then Dallas can waive pierce right after the draft (as long as its before 6/30), and they'll only have 32 million or so in actual salaries, with cap holds that I don't really understand. They should, however, be in a position to offer 2 near-max level contracts, ala Miami.