If we trade Rondo, it takes us at least a year to rebuild our offense. Aside from the heart, the hustle, the speed, and the toughness that Rondo brings to the court, the largest advantage of having Rondo on the court is that he brings Doc Rivers with him.
Rondo is phenomenally intelligent, he knows all our plays, and has shown to know many of our opponents plays (like the entire Heat playbook). He's our coach on the floor, and has a better understanding of how to run his team than a lot of head coaches do. Even bringing in a top-three point guard will upset that in the short term. Any trade involving Rondo means that the window is closed.
The only players that I would trade Rondo for (D-Will, CP3) simply will not be traded for Rondo. Rondo is therefore untradable unless some GM loses his mind.