It really depends on the situation. If the event is large enough to cause anarchy and chaos, it will likely take some time to reestablish order to the
whole country. I would guess that it would collapse much sooner than reintegrate.
The countries are too large to just say, "all clear" and every comes out of their hole. Likely there would be areas where civil communities form.
There would also be territorial and roaming gangs. Some areas would form local governments sooner than others. It wouldn't be clear cut throughout
the land until a long time, IMO.
The severity of collapse and damage to infrastructure would predict the time to recovery as a large governed body. Since we don't know those details,
we can't really predict the outcome.

