Frankly, if my city gets Nuked, the viability of my business is probably going to be somewhat in question, in any case. My ability to recover my up to date accounts receivable data will probably be more than a little redundant, when all of those debtors have been vaporised, money is worthless and, if by some miracle I'm not dead or dying of radiation sickness, I still have access to an electricity grid, to run my computers.
If you're running anything smaller than a country and "nuclear war" is in your contingency plans, you're probably focusing on the wrong concerns.