This will not ever, ever, ever happen. But if the Celtics really wanted to take one last swing with this group AND rebuild through the draft, they could call up the Suns.
Sorry in advance if this has been floated elsewhere.
Step 1: trade Rondo and our 1st rounder (if necessary) for Steve Nash and the Suns unprotected (lottery) pick. Allows the team to make one last run for old time(r)s sake
Step 2: after the season amnesty Pierce (as a favor to him), release holds on KG and Allen and totally, completely start from scratch
you'd have two picks (1 lottery) in a very good draft and you'd essentially be starting over as an expansion team
Ainge has already said he doesn't want to build through the draft, so again, this is fantasy, but interesting that it could be done so "easily"
shoot, we'd have to sign free agents just to get up to the salary floor