I do see your points about the resilience, but to assume total population collapse is IMPOSSIBLE is wrong. Many species on this planet have become extinct and we are not immune to that, locally nor globally. The amish may struggle when crop failure and extreme weather becomes more common place due to changing climates or pollution levels. They might make a bad year or two, but several bad years in a row could significantly reduce populations, possibly to the point of poor genetic diversity where after a few generations certain diseases or conditions wipe them out. They could also just be murdered by hungry stragglers of modern society armed with assault rifles that take their farms without knowing how to sustainably run them.

And also those amish will still have to be having kids despite how bleak their future looks which was the ultimate point of my comment. No kids = no humanity.