I don't see why trading Rondo for a free agent makes sense in any way, shape or form.
Why wouldn't it, if the return in a sign-and-trade was Lebron or Wade?
We have a great young PG, but he's not close to the best player in the NBA.
When has a young player anywhere near as good as Rondo been sent away in a sign and trade deal?
When has a young player anywhere near as good as Lebron been involved in a sign-and-trade deal?
If the Celts have the opportunity to get Lebron (and I doubt they do), they should gladly surrender Rondo. Since there are multiple teams that can sign him outright or offer .Cleveland alluring packages, it's pretty likely that Rondo would need to be involved.
Cleveland won't own his rights. We're just giving them something to enable us to offer him more money. They'd be losing him in any case. Say we offered them a re-signed Ray, Davis and 3 first round picks? If they take it, they get those assets and Ray would be a valuable trade chip. If they refuse, they would likely lose LeBron for nothing. If he had a year or more left on his contract and Cleveland controlled his rights it would cost you Rondo, but not in a sign and trade.
And, obviously, I agree it won't happen, but players like Rondo don't get traded to facilitate sign and trades.