I believe, if the total collapse occurs soon, that there will be fairly quick die-off of human life on the planet. The survivors will make it through the initial tough times and individuals, families, and other small groups will hold on and then start rebuilding their local area. As more and more do so, larger groups, still with highly independent control of their own assets, will form, as durable infrastructure begins to disappear and people realize how much easier life is with at least something similar, and begin to rebuild large local areas and then regional areas.
While I do not believe that it is possible to revert back to the 1800s, 1700s, 1600s, or 1500s in the way that some have postulated. Once created, most of the information and techniques to accomplish things will still be around. Electricity, both AC and DC. Computers. Air conditioning. Paved roads. Bridges. With electricity, computers, and the ability to build roads and most importantly bridges, a set of regional societies will again form into a national society.
I do believe it will be based around the constitution, probably re-written to incorporate what we have learned are the weaknesses in the original. Those being many of the limits of human understanding and the propensity of humans to do only as much as they need to in order to have the best life possible. Hopefully, the safeguards in the new constitution will make sure that terms such as "We hold these truths to be self-evident" are given better explanations because currently, far too many people do not see these truths as truths at all. An actual definition of 'infringed'. Actually, a full dictionary or some type of list of all key words used in any document.
I think the process will take about 300 years, give or take. During that time, with the use of some old technology, much of which will updated and modernized, the rebuilding will go relatively smoothly and quickly. Technologies, inventions, and concepts that were ignored or suppressed beginning in the late 1800s, with one example being Nikola Tesla and many of his inventions. There are many others. With the roads having fallen into bad shape, and especially bridges, the construction of vacuum-based dirigibles and the use of directed force propulsion systems will allow transport without need for roads as that and many other things are built by those that have a good library and the willingness to look beyond the old traditional ways of doing things blindly.
With, hopefully, the new government and national psyche of the citizens that have been born since whatever happened took place, and what things were like prior were taught to the children as they grow to maturity, will be far more stable and will be able to understand how society fell apart before and will do everything they can to see that it does not happen again. They will be far more likely to nip anything that tries to crop up in the bud by showing what happened before.
With the acceptance and use of technologies that might be centuries old but are working just fine with the application of knowledge, materials, and techniques now available, the reconstruction and development of the nation will start slowly but then will begin to flourish as more and more people begin working together for the same goals.
In the same manner, during the next 200 years or so, directed force 'engines' will be attached to recovered and refurbished nuclear submarines for the first few flights off earth. Once proven, purpose-built space ships will begin to travel further and further out. Mining of the resources available in space will take place and communities will begin to develop on suitable planets, moons, asteroids, and purpose-built planetoids.
Five hundred years in the future humans will be amongst the stars, expanding our civilization, concepts, ideas, and everything else to wherever we can get to and survive.
I think we could already be there if so many inventions, ideas, methods, and concepts had not been suppressed by those that are currently orchestrating what is going on right now around the world.
Just my rather fanciful, rambling, and somewhat optimistic opinion.
Jerry D Young
Hope for the best, prepare for the worst, and always remember TANSTAAFL
("There Ain't No Such Thing As A Free Lunch" Manny, from The Moon Is A Harsh Mistress by Robert A Heinlein)