Let me start by saying I love Rondo, and have since the day we acquired him, but I'm not sold that he will be able to play at the level we have gotten used to in the post big 3 era. The reality is he is a great passer but he has little offensive game. If we already had one or two dependable scorers already on our team that could eventually take over from the big 3 I'd say keep him but we don't.
Rondo's trade value is at an all time high so I propose this trade:
Rondo for Steve Nash (and whatever filler to make it work, possibly BBD in S&T)
This gives Phoenix an established PG who could flourish in their up and style type of game, on a pretty friendly contract.
Steve Nash gets a legit shot with the big 3 at the championship, and if we don't win his contract expires.
This gives us a mountain of cap space to pursue Chris Paul and Dwight Howard, then re-up jeff green or let him walk and go after another swingman.
Personally I don't think D12 or CP3 are gonna end up here, but I think this is a good scenario for all teams and players involved.