if we assume the lowest capacity tesla model S and a beefy AC that consumes 5 kWh/h, that's still 15 hours of non-stop balls to the wall AC usage.

Also, provided that you live close enough to a charger that is functonal, you have the ability to drive there, charge your car, and use the energy at home. That's probably less efficient and definitely more of a hassle than just having a backup generator and some dunks of fuel, but hey it's nice to have extra options.