almost as if you were writing a novel.
Do you mean all of a sudden all schools, public, private, and parochial close down? All police and firefighters somehow disappear completely?
Those things in and of themselves would be part of a total collapse of society, and you can write the scenario that causes that.
For the past fifty years or so various people have been predicting the total collapse of everything and I personally think that all of those predictions are quite overblown.
Larger classroom sizes are not in and of themselves a total disaster. My best elementary school year was sixth grade, when there were forty of us in the classroom. My class was the larges of the four or five sixth grades in that school, although we were tracked (a concept that has fallen in to disrepute) and my class was by far the academically best. However, in that long-ago semi-paradise, the kinds of kids that today are special needs kids simply didn't exist. Kids with Down syndrome didn't go to school. Kids with even moderate, let alone serious physical, emotional, or other disabilities likewise either didn't even exist or certainly did not attend public school.
The underlying aspect that you've brought up, the interconnectedness of everything is very much the point. If we fire a lot of teachers, fire-fighters and police, all those now not working people will have no money to spend, and that will reverberate through the economy. It's exactly what made the Great Depression so terrible, and those making decisions to fire the various public employees clearly have absolutely no knowledge of the past.