Ultimately, I think this does not get done before the deadline for the extension and I think both sides will be happy with that.
I think the Celtics want Rondo to prove it to them that he is mature enough and good enough to be the financial cornerstone of the future. If he does, they will have no problem giving him a max deal next summer or matching one. If he has less than a stellar year they will be more than happy to extend him at a lower price or move him. Without a stellar year and given the economic environment, other teams are going to be less likely to offer something big.
And I think Rondo and his agent will also be willing to allow the deadline to pass because I think they realize that Boston will not be giving him a max contract now and I think they believe they will be leaving money on the table by settling now for something less. Rondo is a very confident guy and if he feels he is going to have a huge year and has the possibility of being an All-Star and a two time world championship starting PG before the age of 25, he's probably wise to let the deadline pass and play like a maniac for a max deal.
Either way, I think both sides are smart to let things wait until next year.