Rather than considering it in terms of fatality rate, consider it in terms of curtailing humanity’s possible expansion into the universe. The Industrial Revolution was possible because of abundant coal, and the 20th century’s expansion of technology was possible because of petroleum. The easy-access coal and oil are used up; the resources being used today would not be accessible to a preindustrial or newly industrial civilization. So if our civilization falls and humanity reverts to preindustrial conditions, it stays there.
Rather than considering it in terms of fatality rate, consider it in terms of curtailing humanity’s possible expansion into the universe. The Industrial Revolution was possible because of abundant coal, and the 20th century’s expansion of technology was possible because of petroleum. The easy-access coal and oil are used up; the resources being used today would not be accessible to a preindustrial or newly industrial civilization. So if our civilization falls and humanity reverts to preindustrial conditions, it stays there.