As it stands, the central government has more than bunkers and bottled water in the event of war. From defense, backup communication/power to food supplies, there's no reason to think walkers are going to shut down everything, or that those in command and subordinates are all going to scatter to the winds. Containment would be the first objective--for as long as it could last. ...unless you have a disciplined group beating down dissidents (think Shane). Even Woodbury was free of true internal conflict until the arrival of Andrea and Michone.