Possibly, but not probably. In every protracted event of power being out, there has always been an increase in births nine months later. Most likely, the nation would repopulate itself with our own people.
The longest that I have been without power, natural gas or electric service, was during the period and aftermath of SuperStorm Sandy, from October 29, 2012, to the day after Thanksgiving. We were one of the last areas to have service restored as we were hit with the brunt of the flood. I found it peaceful and quiet without power. Early to bed. Some people were walking around shell shocked. If a massive nationwide or regional grid outage, after a day or two, people would be on foot. Savagery, might take place in some areas, but not in all areas. People, are the difference.