Maybe what ~74,000 years ago (Toba eruption)? Okay, now how would this look in the age of industrial societies and modern nation states? I don't think it would fare well at all.
Probably the only realistic "modern" idea we have is the novel "The Road" by Cormac McCarthy. Although maybe this is too bleak, even under extreme duress humans still show resilience + compassion toward others even while enduring human horrors.
People have kind of mythologized nuclear weapons far beyond their reality. One of the arguments against the use of nukes in policy circles is that this mythology is useful. The limited adverse environmental consequences in practice if demonstrated will greatly lower the threshold for subsequent use.
It might set society back a century, but with substantial knowledge of what was lost. Extinction from nuclear weapons is not remotely plausible.