This is not a question about whether or not any such players might actually become available.
The question is, what players on their current contracts, are good enough that if they should magically become available for trade, the Celtics should try to acquire them and shift from rebuilding mode to reloading?
Let's say the package you would have to give up is Kris Humphries (if his salary is need to match), either Jared Sullinger or Avery Bradley (but not both), one of MarShon Brooks or Jordan Crawford (both if necessary), and multiple first round picks. And pretty much anyone other than Rondo is negotiable.
For example, if John Hollinger convinced the Grizzlies ownership that Zach Randolph should be traded because he is about to turn 32, would you be willing to trade Humphries, Sullinger, Brooks, and multiple first-round picks for Z-Bo if you also had a shot at trading Bass and a pick for a center like Marcin Gortat or Omer Asik? That could result in a starting lineup of Rondo/Bradley/Green/Randolph/Gortat with a bench that includes Lee, Wallace, and Olynyk.
If you don't understand, this is my roundabout way of asking how many current players are "franchise" guys that you could pair with Rondo, because that's how I roll, but don't be surprised if some of the names that people come up with become available for a trade between now and next summer.