Rondo is not going anywhere unless we get great value for him, and by that I mean a very talented player, a superior player. Rondo is currently in a cheap contract, no way he's moving even if he becomes disgruntled.
In any case, I highly doubt that Ainge's goal is to build through the draft, I think he'll be actively trading for talent and the accumulation of 1st round draft picks will make this a probable reality.