I hate to see that show get cancelled.
There's always a petition going around after good shows get cancelled. I don't remember one instance where it has worked. The best I saw it was when the remaining eppisodes of Wonderfalls were released on DVD with the whole season.
My pessimistic view here....
The show started out with almost 11 million viewers and after it's hiatus, it came back with 8 million. Over the remaining episodes, it sank to a 2 rating meaning about 2.2 million people were still watching it at the end. I doubt a petition with let's say 30,000 signatures even makes CBS blink their eyes.