While Rondo trade talk is rampant right now, Danny always: a) takes the long view; b) tries to grow his assets; c) is not sentimental about his players.
With that in mind, a Pierce trade is coming. Given the difficulty of bringing free agents to Boston, you'd have to think that Danny's strategy over the next couple years is going to be to stockpile young assets and picks, and either wait for them to get good, or, more likely, cash them back in for star-level veteran players who don't fit in their current homes.
If you think about that way, having Pierce and Rondo for the next two years really makes no sense -- it improves your record, which worsens your position in the lottery -- and it wastes Pierce's last two years without getting anything back.
On the other hand, if you trade Pierce now, you could get a couple young guys + picks, which both accelerates the rebuilding process, and makes you worse next year, which gives you another good pick.
I think he'll try to do the same with Allen and Garnett, but the challenge there will be not to take back bad contracts. But my guess is that come March 16th, we will have a very different roster than we do today.