A vast majority of modern people would die a helpless death relived of their modern inconveniences. You don't get time to "learn" how to farm when you don't have any food.
And farming is only 1 or 2 generations removed. Give it a few more turns, and one can easily see the world in the story becoming a reality.
I've lived on a farm for a couple of years (in Ontario), and it is simply amazing how much hard work goes in to making a piece of land productive, even with modern tools.
In aerodynamics as applied to jet aircraft they have something called the coffin corner, a speed so close to the limits of the flight envelope in all directions that a small change in velocity will make you either stall or break up.
It's possible that there is such a thing as 'societies coffin corner', a speed of development so great that if it gets exceeded by a little or drops for a short time that we'll literally crash.
Vernor Vinge's stories have addressed a very similar idea. "A Deepness in the Sky" has significant interludes on this topic, though it's not the main focus of the work.
And farming is only 1 or 2 generations removed. Give it a few more turns, and one can easily see the world in the story becoming a reality.