Rondo would have been foolish to extend this past offseason. waiting until the coming offseason makes so much more financial sense for him he'd have to fire his agent if he recommended signing.
I know that is the conventional wisdom or thinking but I actually don't agree that it is that black and white. Think what kind of contract Rondo will end up with if he reinjures his knee? Would he have been foolish then for adding on 3 years and around $45M? How about if he continues to average 6 pts a game (as he has for the last several games) or shoot 30% from the line?
He could have signed for the extension and been set for life (double set actually since he probably is already set for one life). He could have included an opt out half way through so that if he didn't like the team the Celtics put together or if he wanted to cash in on improved market value, he would have been able to do that. Or if he got injured, he would be set.
We are probably talking about 1 year (3 year extension or 4 year new contract) probably and maybe 2. To me, playing this season on a bad team, after a serious knee injury, is a lot of risk to get one more year out of your contract.
With Rondo, I don't think it is about money. I think he wants to be a free agent and "play the field"; be in control, choose who he plays with and where he plays. That is his prerogative but there is plenty of risk with that choice.