It doesn't take that long for people to become frustrated at a lack of services they depend day to day on thoughtlessly. Also energy delivery systems that traverse state lines are not a city tramway.
Indeed. If the city loses its power, others will help. Trucks will come shipping food. If the whole power grid goes out, there won't be neither food nor enough fuel for truck to ship it.
https://en.wikipedia.org/wiki/New_York_City_blackout_of_1977