I imagine there may have been times where a team had a bunch of old dudes that "rode off into the sunset." But for the most part, teams that make it to the conference finals are competing for a championship (yeah, I know we weren't getting past Cleveland or Golden State, but you do have to think you're closer than an 8th seed).
So how often has a team in the championship hunt just blown it up and replaced four starters?
It should be noted that no team in the history of the NBA has had as many assets and had as much cap room as the 2016-17 Boston Celtics. Seriously, that's a once-in-a-lifetime situation where you fleece a team as badly as Danny fleeced the Nets and you fall into a trade that nets you an All NBA 2nd Teamer for peanuts (IT), you get two All Stars in free agency in two years (Horford and Hayward), and you have enough high draft picks and tantalizing players (Crowder, Zizic, and the Nets 2018 pick) to get another All-Star (Irving).
Heady times we're living in!