At which point - then what? None of the major atomic powers has enough (if any) missiles left to be much of a deterrent, and none of them will have armed forces that are any more prepared to do an Atlantic or Pacific crossing and invasion than they are now. So it's just that much worse for everyone?
Nobody spends more on defense than US. Also, the new technology that you hear about today is essentially declassified tech from ~20 years ago. I remember reading in the past about Boeing doing experiments with a 747 carrying a giant laser that could lock on and fry ICBMs. There was also stuff like this 14 years ago: https://www.youtube.com/watch?v=KBMU6l6GsdM
Extrapolating to today, I firmly believe that US (and probably NATO and other countries who share intel) are watching Russian launch sites closely, ready to drop kinetic warheads from orbit at the first sign of activation, not to mention multiple layers of defense with kinetic kill vehicles, lasers, EMPS, jammers, e.t.c. That is assuming, we don't have stuxnet like malware hiding in computer systems that would just magically cause the missiles to fail.
After all, Russian military was shown to be wildly incompetent (which US probably already knew), so that translates to easy infiltration/intel and creation of a safeguard plan to counter anything they have.
That being said, humanity will go on. Even if the entire nuclear arsenal was detonated like a fireworks show gone wrong, I highly doubt all places on the earth will be affected. Hell we've been hit by a massive asteroid once, and life still went on. Highly doubt a few thousand nukes going off will be any close to that bad. Also its not like they're gonna nuke the shit out of Africa, S. America, or some pacific islands. Even if nuclear winter will suck and what not, again - some people will survive and for me personally that's all that matters.
I'm not one of the uber rich (and no I don't mean the trust fund kid nor the startup founder who had a 9 figure exit), so I don't really care nor know what they'll be doing. But I'm sure some of them will already have prepared for this scenario. If I was uber rich, I know I probably would have.
Most of us plebs will most likely perish. I will most likely be one of the first ones gone because I live in the bay area.
Some of us will survive though. Instead of slinging infrastructure or loading up test data, we will be forced to survive at all and any costs. If I survive, I am taking zero chances with people I don't know or trust. My water, my food, my shelter.
Again, no hard feelings and I have no expectations from others- I want to survive as long as possible because why not... Until we have a New California Republic or something like that, on God zero chances. Plus, it would be cool to rebuild.
End of the day, its just a game for better or worse. Might as well play it. I might get in a car accident and perish later today lol in which.. no ww3 for me.
One factor is that don't need that many missiles for retaliatory strike; a single SSBN would be enough. The place where calculation could change is first strike since that takes lots of warheads and would leave attacker depleted. The other issue is keeping uninvolved country from launching, better tracking would help with that. But is good argument for not having nuclear war.
Also, there wasn't much thought about strategy after nuclear war. I think it was assumed that the decision makers and most of their countries would be dead. Collapse of civilization and nuclear winter would mean that survival is the focus. Nobody will be worried about "imposing their will" but not starving.
I'm not sure how much worse mutual assured destruction could get by going over what they already have.
Though I see it very likely that thousands of nukes will fly, under the 'use it or lose it' policy.
Those that don't die immediately will wish they had.