The cities are absolutely going to invade the surrounding countryside. Mobs and gangs of hungry people banding together to take what they can from weaker neighbors has been a feature of nearly every instance of state failure.
As a city-dweller, your strategy for surviving this is to join one. As a wealthy suburb dweller, you better hope you have a private security advantage where you can kill the whole mob before it kills you. As a rural dweller, your strategy is to be far enough away, high enough up, and insignificant enough that it's not worth going after you. Gas will be in short supply after a collapse; it's not worth driving 100 miles to take food from a farm that you don't know exists. Most of the towns and small cities in the regions I mentioned are easily that far away from the nearest city.
It's pretty likely that the dominant political organization after a national collapse would be city-states. However, that doesn't mean that it's best for an individual to be within them. We might see 75% depopulation within cities, but people in rural areas can go on about their normal business, if they don't get conquered entirely by the local city. It's a choice between living in privilege in the aftermath of the collapse but having a good chance of not making it there, vs. a higher chance of survival but you'll be a vassal state to the local city.