We have recently upgraded our diesel fuel tank for the apartment complex generator (tripled the size). So at least we should not be stuck in elevators, and our public space lights, water pumps, and entrance/exit gates will be functional for quite a while. Also we have huge cellars under each building with per unit cages, it's quite cold there, so we can store some perishable food for the recovery period.

For the electrical grid cybersecurity, it is quite possible that the author simply has no good enough grasp of the network security measures and secured network architectures available and implemented. Banks and online shops are no good as an indicator at all, as they have to be wide open to the public and other businesses to work properly. Just use an Intranet without any physical Internet connections and you are safe as long as you don't have a sabotaging spy among your employees. But that worked perfectly during millennias of pre-cyber era.