The gas fireplace typically only requires a fuel line from an operational standpoint. So in short, if you have a modern gas fireplace you should be able to operate it in the case of a power outage.
The exact answer will much depend on the specific unit you have, but if you take a look through your operational manual, you should be able to find an answer.
Modern fireplaces have a manual override in the bottom of the firebox (the access tray) that lets you switch the electronic ignition to "on" or to the "run" function. A typical Superior Fireplace unit has a battery backup function that will provide a safe pilot light ignition sequence so that you can use your unit. To see how to operate your fireplace in the case of no power, please refer to your operational manual, or search your model number online to find it.
Your limitations in a power outage will be the internal fan. The fan is designed for optimal performance of your unit, but not for basic function. This means that your gas fireplace will be able to run but will not perform its best. In this case, you will be glad to know that you can use your fireplace in the case of a power outage, and have a dependable source of warmth for your home.
Please feel free to give us a call if you need an additional product manual or need helping finding your product model number.