Hate to call ya on this one, but plenty of United Express and American Eagle flights I've been on have either zero or one FA... In the case of zero, the captain or 1st officer comes back and does the safety demo before the flight. And in the event of an evacuation, I imagine they'd be responsible for getting everyone off as well. The zero FA flights are UX flights on the BAe Jetstream 32 props, which seat 19. The 1 FA flights are slightly larger planes, up to the 50 seat Canadair CL65 regional jet.