To the OP: I understand your concern for the team's future, but I respectfully recommend just relaxing and enjoying what you're seeing, which is a promising crop of youngsters who, under Ainge's shrewd management, will become (via development or trade) the next great iteration of Celtics basketball. Boston also already has a bunch of good draft picks covering the next few seasons, and could land more by next summer.
As "rebuilding" or "bridge" teams go, Boston is sitting pretty: lots of young prospects, lots of good draft picks, a good coach, and an All-Star point guard who can be the team's centerpiece OR trade bait for other highly desirable assets.
As much as I like Pierce and KG, if they (and Doc) were still here, it would be another mediocre regular season of tired vets and underused youngsters followed by a couple of inspirational playoff games before an early, unceremonious exit. I've had my fill of that, and I love seeing the youth and promise that's out there right now. Since Reggie Lewis died, Boston's had basically one really good homegrown talent—Paul Pierce—and all the other major talent has been imported. I'm not against imports, and I'm sure we'll have more, but it would be great to see another homegrown talent or two (or three) as integral parts of a Celtics title team.