At first, I thought the smart decision was to pass, but...
A Rondo for Lopez-Williams is a steal for the C's... Brook Lopez alone is more valuable than Rondo. Lopez is only challenged by DeMarcus Cousins as the best offensive Center in the league and he's younger than Rondo. If you don't think Lopez is a long term option (whether because of his injury history or his game), he's one of the most tradeable assets in the league and would get a better return than a Rondo can.
Williams might be an excellent buy-low option for teams that are not set at PG. His stock dropped far this year, but players that have shown the ability Deron has don't just lose that without age, injury, and/or lifestyle being significant factors.
It's been reported that he will undergo an MRI on his ankles (note: both ankles...) and might need ankle surgery during the off season. He's missed a considerable amount of time throughout his time with the Nets (Steph Curry had similar issues, but he's an example of an elite player overcoming chronic ankle injury). He also has appeared to be slightly overweight (people usually chalk overweight players to lack of work ethic, but injuries play a part in being able to get in shape).
If the Nets are intent on trading Williams, they better field a good return for him even though his stock is at its lowest because, if he gets healthy, he has a good chance at returning to being a top 30 player. Mavericks, Rockets, Timberwolves, and Knicks might be salivating at the thought.
I wouldn't do it straight up for Williams or Williams and Johnson though... Rondo has more value than both (though that might change if Williams gets healthy) and he's more reliable.