What I question is the realism of the almost instant descent of the worlds population into barbarism. I believe that there would be more of an attempt to organize and survive as a society than Sterling posits. I do not exclude a massive die off, the currant population levels and distribution are clearly unsustainable, and some level of banditry and cannibalism is inevitable. I think it probable that in areas like the US and Canada some level of "state" and even "Federal" government would survive or be reoganized.
My thought and question to others is what is the likely social survival picture in your estimation?
The existing US social order completely collapses in the Emberverse books because Stirling wants it to for his narrative, not because it is the most likely immediate outcome. Obviously, large cities and suburban areas would collapse - there are too many people packed into too small an area with not enough basic survival skills to make it. But like you, I believe most people - including those with the skills and knowledge to survive without modern technology - would tend to coalesce around existing community organizations - city councils, military bases, churches, police departments, or corporations. Each in their own way, these entities would seek to preserve and maintain what they saw as "American Culture". To me, Stirling's whole notion that people would somehow immediately devolve into some sort of medieval mind-set, complete with Knights and pagan tree worship has little basis in the reality of modern America. As displaced starving hordes flee the cities and suburbs I think the majority would seek to fall under the protection of functioning small communities - not eat them - and most of not all of these communities would attempt as best they could to incorporate the refuges in a humane way. It is in fact possible that something akin to serfdom or slavery might be seen as a necessary evil to allow the most people to survive, but it would rarely be an end in itself. I guess I have too much faith in the essential goodness of modern humanity to imagine the total collapse.
That being said, I don't believe the USA as a single federation could survive, nor could most States. Most leadership in all three branches of government at the federal level and in states tend to be located in the large urban areas hardest hit. Plus, virtually all comunication would have broken down. More likely you would get the rise of hundreds, maybe thousands, of small commnities that retained a loyalty to the concept of the USA (and the State of, say Oregon) and who saw in their survival and growth a way to start rebuilding the old order. I also presume that the leadership of most of these statelets would be drawn from governmental or quasi-governmental figures in the pre collapse - police chiefs, mayors, military base commanders, businesses, trade union leadership, chambers of commerce, etc. Such people would be predisposed to ally or join in confederation with other like-minded groups the next county over.
On the other hand, the strong notion of local rule and federalism in the USA would probably make the resurrection of a continental (or even regional) nation unlikely. Over decades and then centuries, the simple fact of distance and primitive communication would lead to the evolution of fully independent states - and probably such divergence in language that "American English" as a single mutually intelligible language would disappear. At that point cultural devolution would set in and you could see the gradual rise of radically distinct social orders, religious systems, kingdoms, empires, and what not across the former USA, but that would be the long-term result of the collapse, not the immediate reaction to it.
I can believe every other bit of this specific post-apocalyptic setting's initial chaos, except the whole cannibal part. It's just way over the top, as if Stirling wanted to write in a bunch of cartoonishly ebiiiil one-shot villains.