Any number of things could result in a prolonged “grid-down” scenario; Electro Magnetic Pulse (EMP) attack, Solar Mass Ejection (SME), cascading infrastructure failure, Black Swan, etc. A geographically widespread, prolonged “grid-down” scenario would result in a catastrophe of biblical proportions.
With the emergency extending over a large geographical area it would exceed the capacity of our nation to meaningfully intervene and people would be left to their own devices. Backup generation capacity, if it was operational would be exhausted within days.
Imagine Manhattan, with a population density of over 47,000 people per square mile without electricity for a period of 6-months or longer.
The immediate inconvenience would be dealt with in the usual manor; lighting candles and dining on free meals of what is considered perishable and otherwise enjoying the “blackout”.
As hours stretch into days and days into weeks the novelty would soon wear off.
Without elevators residents would be forced to walk up multiple flights to reach their apartments. Death due to heart attacks and strokes would skyrocket.
Almost immediately the rate of residential fires would rise dramatically due to the misuse of candles for illumination.
Deaths due to carbon monoxide poisoning would rise exponentially due to the use of charcoal and propane in enclosed spaces for cooking and heating.
Within days potable water would no longer be available anywhere in the city due to the lack of pumping and treatment capacity. Sickness and death due to drinking contaminated water would rise to near epidemic proportions.
Without water, toilets would no longer flush. Without electricity to run the pumps sewers would back up contributing to the health emergency.
Surface transportation would be at “grid-lock” due to no working traffic lights. This would cripple resupply efforts and emergency services in the form of ambulance/fire/police would be delayed or prevented from responding. Trash removal would cease resulting in the accumulation of trash which would further exacerbate the city wide public health emergency. Within days the subway tunnels would begin to fill with water without electric pumps running resulting in irreparable damage to the system and the collection of stagnant waste water throughout the city.
Available food supplies would be exhausted in a matter of days and in desperation spoiled food taken from failed refrigeration units would be eaten resulting in thousands of cases of food poisoning.
The health care system would be overloaded immediately and would fail totally within days.
Almost immediately the criminal element would recognize this blackout to be a terrific opportunity and would go into a “feeding frenzy” of criminal activity.
Pharmacies, destroyed by looters or shuttered for security, would be unable to fill prescriptions and thousands of people dependent upon a regular supply of drugs would die or go crazy without their pharmaceutical support.
After 6-months without electricity even Snake Plissken wouldn’t recognize the place.