"Even with all out nuclear war, there would be someone with technical knowledge that could keep from that far of a backslide."

No, acutally, its really unlikely that any surviving amount of technical knowledge after an all-out nuclear war will keep it from backsliding, at least for some amount of time.

Its like telling Bill Gates that now he has to subsistence farm, or die. Everyone dying everywhere, the destruction, the chaos. How is someone in a radiation-wracked landscape of utter death and destruction going to fall back on technical knowledge to improve his situation? He adapts.

How you work out a scenario is all up to you, you can say, a limited exchange or incidental blast, or all-out nuclear war. Whats the worst case of a worst case of a worst case scenario?

Nuclear weapons are insanity.

The talking heads only mention an incidental "terrorist" blasts as the worst case scenario. Even a limited exchange is too much to consider. An all-out nuclear war is just the cold foreboding of a half century since we invented the weapon and created it, and manufactured thousands of them. They are now all over the world. The talking heads don't talk about it because its the monster right in front of your face. Its too horrible to imagine.

Humanity was never held by a thread like this in all of history.

Maybe the Stone Ages are too generous a comparison, after all, did they need to worry about radiation, or about scarity of food, or, lack of technical knowledge on how to procure these things directly from the natural environment?

The (few) remaining humans of planet Earth will have to start over from scratch. Scratching at the ground with rakes, attempting to till a charred and burnt Earth with a few barren seeds, their bellies hungry underneath a cold, grey quilt of eternal winter.