At this point we're on something like Plan F.
No Butler, George, Griffin ... possibly no Hayward.
Plan F is make moves for short-term supporting players to supplement the "Bridge Core" (i.e. Thomas, Bradley, Crowder, Horford) and try to develop the "Future Core" (i.e. Smart, Rozier, Brown, Tatum, Zizic etc) without sacrificing playoff seeding.
The ceiling on Plan F is what the Celts accomplished in 2016-2017 for the next few years. Once IT and Horford are ready to move on and the "Future Core" has come of age, maybe Ainge tries to make a move to contend again. Or maybe he just flips everybody for future assets and leaves it for Austin to figure out after he retires.