You don't need to survive for a week but max. a day or so. Anything longer and electricity will come from somewhere else in the grid, either a different region or a back-up conventional plant being gas or nuclear or even coal.

At least in Germany even large industrial energy consumers are for years now an active part of grid balancing. Either they can stop and resume production as needed or continuous processes serve a similar function as your base power plants. The silver bullet to get them there was money, it became financially viable and profitable and all of a sudden businesses jumped at the opportunity.

Disclaimer: Worked at two of these power hungry places and know of of another one making quite some money on the electricity exchanges by just timing his production runs properly.