I think this off season is the turning point. This roster has reached its ceiling. The two paths forward are:
1. Successful free agency and trades, or,
2. Blow it up
Let's look at each path.
Most Celtics fans would want Path 1 to work out. Supplement the existing roster with a true superstar and more talent such as Durant, Horford, Cousins, Butler via trade or free agency. IMO Ainge needs to go all out this off-season to achieve this. If he fails the next option is blowing it up.
What does blowing it up mean? To me it means moving on from players that may be fine rotation players but have reached their ceiling (Sullinger, Jerebko, Zeller). These players are easily replaceable if need be. The team should not be allowed to wallow in mediocrity and have first round bow outs. Time to restart the rebuild. Are RJ Hunter, Young, Mickey ever going to amount to something? Let's find out by giving them 20-30 minutes a night.
Accumulate assets. Trade Bradley for a first rounder in a future draft or a young underused player. Perhaps even trade Thomas for a future draft pick or two. Sounds a little like the Philly plan but the roster as currently constructed does not have a legitimate chance at a championship or even a deep playoff run in a weak Eastern Conference.
Players that stay in a blow up scenario:
Smart
Rozier
Hunter
Mickey
Young
Olynyk
Crowder
Everyone else is tradeable.