Even if the growth doesn't last forever, many people are beyond reasonable thresholds. Having made their money, people are downsizing in innovative ways - leaving America for 6 months for a cheaper country, relocating to a lcol place or even casually experimenting with starting another business.

Short of a multi year recession, most FIREed folks will survive. You don't need to get another job when you can just downsize your expenses in bad years.