Consider the departure of Doc Rivers Phase II of the Celtics’ slow dismantling, which began last summer with Ray Allen leaving Boston. Phase III will come this week, when Boston must either trade Paul Pierce or decide to buy him out. They have until June 30 to inform Pierce of such a move.

As for the rebuilding sure to follow the dismantling, that is contingent on what happens with Pierce. If the Celtics can unload Pierce to a team with enough cap space to absorb his salary, they will get a trade exception worth Pierce’s salary, or $15.3 million. And if that happens, the plan is already in place. According to a source, the Celtics have a sign-and-trade offer ready for Atlanta forward Josh Smith that would be the top priority in free agency.

Smith has long been connected to Boston in trade rumors, including one that would have sent Pierce to Atlanta in February. His link to the current Celtics dates back to high school, when he played with point guard Rajon Rondo at Oak Hill.

In order to land Smith, though, the Celtics need to pull off a deal for Pierce that will net them a trade exception. Because teams over the salary cap can’t take on salary without sending back matching salaries, Boston’s options are limited to teams under the cap. That’s why two teams that have been connected to a Pierce deal have been Cleveland and Milwaukee.