Northern Illinois Gas Co. 's computer disaster recovery program can have the company up and running within hours - no matter what. It's not that they are pessimistic; they're just realistic. They know for certain that their company could be devastated by a fire, a flood, a tornado or some other disaster, even though the odds on it are slim. What's more likely is that a less serious mishap could knock out the company's sophisticated computer system, and for a major utility these days, that's the equivalent of the worst catastrophe Mother Nature could dream up.