Let's take a look at the 2011-12 season (the eighth overall) of The Office on NBC.
Rating the Ratings: The Office went seven years without ever dropping more than 7% in a season. The loss of Steve Carell meant that impressive streak was certain to end in season eight, but I still feel like NBC's top comedy could've held up a lot better than this. The season started pretty well, down only about 10% or so year-to-year for the first month, but by November it had become pretty clear that a full-time Carell-free Office was not really resonating. Most data points starting around the beginning of November were down 20%+ year-to-year, and those comparisons got even uglier in the spring since the end of the previous season had so much momentum from Carell's departure. Perhaps even more disheartening than what happened with The Office, though, was NBC's continued inability to come up with any kind of heir apparent. Both Parks and Recreation and once-promising Up All Night struggled in post-Office turns late in the season. So NBC's sticking with The Office at the center of a Thursday night that looks like a big old white flag ratings-wise. Grade: D.
Here's the now updated War of 18-49 post for The Office.