Are you so sure it is external forces that have caused the plateau? What about issues connected to campus enrollment, retention, progression, graduation, etc.? What about physical space limitations?
The plateau we're seeing is very likely caused by a plateau in university enrollment. And as long as new faculty lines aren't forthcoming, I'm content to see our SCH production stay flat.
The purpose of my original query was to help me plan for unfortunate external events in the future--e.g., if popular movies and TV shows suddenly start depicting practitioners of my discipline in a negative light or my discipline becomes the latest "major that gets you nowhere (or to an unsatisfying salary)" in popular thought.
I appreciate the suggestions made so far--especially the reminder about the value of getting courses into the gen ed curriculum. Any more suggestions?