If it's true that there are NBC suits that love the show, there's a good chance at renewal despite the crappy ratings. And Yvonne Strahowski said in her "finale" interview that they were planning this finale to set up a great "final season next year," so maybe the producers will use that as a bargaining chip:
"Hey guys, you love us even though are ratings are low, but if you renew us we'll wrap it all up next season."
Could work.
If not, it's Farscape all over again (without the 4-hour TV movie ending).
Honestly though, their ratings really aren't that bad by NBC standards. They do better then Heroes sometimes. They do better then Parks and Recreation. They do better then My Name is Earl. They do better then Friday Night Lights. They do just as well as 30 Rock. And all of those shows have WAY less competition in their time slots. You put Chuck on Thursdays or Sundays, watch the ratings go up.