If Danny manages this team properly we can extend our run as an eite team for another 10-15 years. Rondo will become the third best point guard in the league in the near future. Within two years, to be sure. Perk is also a very solid center, who, at least for now, comes to us as a bargain. As long as we resign Rajon and Perk, we will have filled the two most imporant positions on the floor-- center and point guard-- with an all star and a borderline all-star center (I'm speaking of their status as players down the road, obviously).
I think this is probably too optimistic. First, I think it's doubtful that Rajon will be the third best PG in the NBA; in my mind, he's clearly got a lower ceiling than CP3, Deron, and Rose, and there are several other guys who are on or about Rondo's level. As for Perk, I don't think he's a centerpiece. Even if he's a top-10 center, I'm not sure that a borderline all-star and a solid center are enough to make a team a perennial contender, especially when there are basically no other young, proven pieces on this roster.
I think this team's guaranteed window for championship contention is until Ray's contract expires. After that, the team should remain solid so long as PP and KG are still on the team, but without a third star, I don't think those two alone will be good enough for this team to truly contend. Danny can extend that window, of course; Ray may resign, or the team could acquire another star. However, as things stand now, in my mind the window is this year and next.