Also society isn't going to collapse overnight.
That’s the other thing. Society is more likely not to collapse, but just adapt. Half your country could be wiped out by a nuke. If the capitol was taken out then you’re just entering government less warzone like Darfur. They still have trade etc in those regions. Eventually surviving external government exert influence and prop up their preferred government.
Or the capitol survives, the housing market crashes, everybody becomes poor, disgruntled young guys force through a vote for a strong daddy to lead them through this tough time.
The movie “the road” is horrible but unlikely. The Last of Us military city states is more probable. Or just reading a history book.
Reminds me of a billionaire who went “woke” because he did the research and realized it’s far far far more effective to just start building farms around his home city then building a fancy bunker for him to die in. Actually building public infrastructure with redundancy.