Dallas won because of their bench depth that helped with Barrea and co. Boston doesnt have heroic bench players like Dallas. That small forward/SG they got from Thunders or Jason Terry and Barrea come on ;)
CP3 and Rondo is too near in their overall ability to do Boston any good in long term even if they could get Paul.
Boston have no choice to build a new team. You cant dump the best assist player of last season who is a great rebounder,defender and who is younger than Paul. They need him most.