I don't know, after Jericho, I think it's going to be a lot harder for a show to be saved, no matter the outpouring of fan support and effort.
Based on the lack of organization towards any "Save Numbers" effort, it's fair to assume that a lot of fans of the show feel that it had a pretty good run (6 seasons) and everything has to end sometime. I liked the show too, but it's clearly had better days. If it was on any other network, it would have stood a much better chance of returning, but CBS has such a deep bench of popular shows that they cancel any show that isn't pulling its weight and replace it with something that likely will.
My only regret was that it didn't seem like a true series finale to me. By that, I mean that you could tell that the writers were clearly hedging their bets in case the series does get renewed.
I agree. I felt like it lacked as a series finale. There were a lot of different elements in one episode; and the David leaving thing seemed to come out of nowhere, either this episode of the one before (I can't remember). But it seems like since they cut the episode amount down, they just threw a bunch of stuff to attempt to resolve everything. I know they aren't the central focus of the show, but things feel unresolved with Colby, Nikki and Liz; talking about a partnership with all three of them and what not.
I suppose it's good to end on a good note, but one thing I liked about this show was that it dark like some of the other crime shows. Numb3rs had some comedy built in that I liked. I also loved the relationship between the father and sons. I don't think it would have had quite the same vibe without their dad. I'm sad to see it go.