Amish Paradise

 The Amish are known for a peculiar way of life that is quite a complex orthodoxy that often comes down to the simplification "people who avoid all things modern".

Those who embark on "civilization collapses" fiction can be of two minds on the subject. On one hand, they would not directly feel too much of a pinch from a world that is no longer industrialized. On the other, such an upheaval would probably create roaming bands of marauders, and their pacifism would put them at a severe disadvantage. 

This may be a "truth is somewhere in the middle" situation. Their fundamental understanding of farming and craft would be immensely useful knowledge in a world that has to relearn all these things. The most pragmatic of said marauders could certainly make some kind of deal with them for goods, a truly pragmatic (and maybe somewhat compassionate) marauder would  arrange for some kind of learning exchange, and make sure nobody else touched them. Those Amish may, to some degree, agree, though it may come with some strings to perhaps call ceasefires, or attend their services once a week.

This couldn't last forever. Sooner or later society is going to become too belligerent, or desperate, and with their skills eventually no longer being unique, their protection will probably disappear. Or perhaps we will just see a society gradually and naturally blend into their surroundings, as many cultures do. The Amish, as a distinct cultural entity, will not exist as an entity by 2900. But if they're fortunate, Medieval America will have learned something from them.