Or maybe the C's can trade Rondo (and other pieces) for Westbrook in the offseason. This is where the lack of BYC rules in the new CBA could be very beneficial, because it makes it much easier to trade for him, even though he is already extended. If they underachieve in the playoffs this year, and Westbrook doesn't work well with Durant and company, perhaps they consider moving him in the offseason for a cheaper guy in Rondo, who might be a better fit with scorers like Durant and Harden.
If they keep Westbrook, it could really tie their hands with signing Harden, and still staying below the stricter luxury tax in a couple years, but Rondo would make it easier for them to swallow.