It reminds me of the short-lived sci-fi series several years ago called "Revolution" in which all electrical power suddenly stopped working everywhere on earth. Fifteen years after it happened, living conditions and even some clothes resembled something out of the Civil War era.Not far from true. If the power grid got knocked out, basically putting us back in the 1870's... some of us would survive. But not very many.
That's why I consider Kirk's actions at the end of "Spock's Brain" to be virtual genocide... turning people who lived in a tech society into essentially cavemen rarely ends well.
Kor