A lot of places (including homes and some hospitals) now use natural gas as their preferred fuel for running generators in power outages. This means they rely upon it, which in turn means the natural gas companies have to be able to deliver during power outages.

With this is mind, it depends on your individual utility provider. I would give them a call and ask what preparations they have in place in case of a power outage. Sometimes they don't like to give that info out, but if you explain that you were thinking about running a natural gas emergency generator and wanted to make sure it would work effectively, they might be more forthcoming.

I know, for example, my local gas company installed four turbine based electrical generators in 2007 specifically to provide backup power and to reduce their electrical consumption costs.

Also, one thing to keep in mind, regardless, is that...pipes break. If a natural gas line that feeds your house ruptures, than your service will be interrupted until it can be fixed (just like if a power pole gets knocked down and takes out your electric lines). Therefore, it's best to have multiple methods of lighting your home, cooking your food, and keeping yourself warm available to you. You never know when you might loose all your utilities due to some kind of freak disaster (earthquakes are good for this).