[whatbutwhy]

Definitely. I'm not sure how you'd expect anything at all to function without power, water, food, messaging, etc would all be gone. I'm not sure how it'd be possible to survive if you're in a city.

[jjeaff]

It wouldn't be ideal, but cities have been without power for several days if not weeks before.

[mekkkkkk]

Aren't those cases mitigated by receiving support/supplies from elsewhere though? The thing about a massive solar flare is that this "elsewhere" would be facing the same issues.