Thinking logically, each state’s governor becomes the head of state in the event that the federal government falls. 50 separate nations would be the result, with infrastructure inside each state to mostly sustain that state’s needs. There are of course things that only the federal government does at this juncture. State’s governments are designed this way on purpose. You don’t have a state board of elections that handles all the states elections. You don’t have a state department of transportation that handles other states transportation needs. Its pretty much like the other person stated. Even the military is somewhat accounted for with state national guards.
Other than Texas no States have their own power grid every pne of them is dependent on the synchronization and frequency control of the others over continental sized distances. Oregon powers much of Washington State, Arizona does a huge chunk of California. Tennessee powers most of the state’s that border it via the TVA. The examples keep going.
Water is even a bigger nightmare especially the desert southwest where the dams straddle state lines and Colorado is up stream from 30+ million in California Arizona and Nevada with the snow pack that feeds the mighty Colorado river system. The Mississippi river system is more of a nightmare it splits every state it runs through almost. The regional state to state wars over resources would make the Kosovo conflict look like a snowball fight. The death tolls from starvation and tribal style retribution plus desporate resource battles will be biblical in scale.
Its all mental masturbation anyways since no one is going to give up the house and mortgage payments , give up the truck and boat, lose their precious job, and all digital assets held in computers by banks scattered around the several states. ALL of those things would be lost day one of any real battlefield. You would be starting from scratch assuming you survive the conflict,mass starvation and the scorched earth that followed it. A lifetime of assets would evaporate in days , “the wife” if she is still alive by the end and not taken by a regional warlord would be very upset to say the least. No it’s delusional fantasy to think a 1776 or even a 1865 type battle could be fought by modern people with modern weapons. Remember they did say F15s and nuclear weapons that was not hyperbole one side has them and certainly will use modern massed weapons on the other bank on it than includes tactical nukes the rest of the world with nukes would cheer them on there is no danger of Russia or China stepping in if nukes fly here take that to the bank.