As Doc Rivers was coaching the Bucks against the Celtics Monday night, he could look up to the TD Garden rafters by the Bucks‘ bench with pride. That 2008 NBA championship banner? He’d helped hang that thing. But along with the satisfaction, there can also be a measure of wistfulness for Rivers in the skyward gaze. Since he left the Celtics’ sideline in the summer of 2013, there has been a resurgence here that culminated last spring in the club’s 18th title. Had Rivers stayed, he would likely have his own chapter in franchise lore. He could be well on his way to a spot on one of the retired numbers flags — perhaps with the total of his Boston wins after he retires, or maybe DOC written in descending diagonal order as with the LOSCY for former Celt Jim Loscutoff.