I'd only trade Pierce if he was Ok with it and wanted to go compete for rings somewhere else during his last few seasons, rather than grinding it out on a rebuilding team.
If Pierce wanted to stay, I'd honor that, make use of the Cap space I get from KG, Ray, O'Neal, Bass, Marquis, Wilcox and Dooling's expiring contracts and incorporate Pierce into the mix as usual.
However, the following scenario works very well for me if Pierce wanted to go:
Clippers:
Pierce, Wilcox and Dooling for Butler, Mo Williams, Beldsoe and Thompkins.
* Thompkins and Bledsoe are good young player pieces
* You cna Flip Butler for more young talent in the off season and Williams is tradeable next year for additional picks of young players
Pierce gets to go home and play in front of family and friends with Blake Griffin and Chris Paul - hardly a punishment for him. He's knows his number is getting raised here.
After the Clipper's, now owning the best "trio" in the game in Griffin, Pierce and Paul, raise a ring or two, Pierce's Jersey might get raised in Staples center as well.
Celts young nucleus, moving forward:
* Thompkins, JJJ, Bass, Jeff Green, Bledsoe, Moore, Rondo
* Butler and Williams flipped for additional young talent
* Two draft picks in this year's draft
* Major Cap space available for max free agents as they come available
If you work that right, you'd be suprised how quickly you could be back in contention.
It would hinge on being able to land 1-2 max guys with your cap space and maybe getting lucky in the draft.