If the network wants to kill a show, they can create circumstances where it will fail. ABC did this in 1979 and 1980 with Battlestar Galactica. The show was doing well in the ratings, but the bean counters killed it due to its cost.
A Letter writing campaign from the fans got a reprieve in the form of Galactica 1980. Which ABC promptly moved to what was known as "Family Viewing Hour" at the time, an attempt to avoid govt. censorship of content. So, after the first episodes, it was all child-centric stories such as "The Super Scouts" where the kids were the heroes of the stories. Needless to say, it collapsed in ratings, and was cancelled for that reason.