It's Already Cheated Death Once
Pop culture tends to overstate the effectiveness of fan-led campaigns on behalf of struggling shows. Rarely do these calls to action work. Usually a third corporate party (Subway for Chuck and DirecTV for Friday Night Lights) is required to get a deal done.
If a show does receive a miraculous intervention, lightning won't strike twice. After a show is saved by a grass roots campaign, the most fans can expect is two additional seasons, and even that requires extenuating circumstances, like NBC's abysmal ratings.