http://quaketips.blogspot.com/2013/05/should-i-turn-my-gas-off-after.html

This and other sources suggest that turning off the gas should not be done in a knee jerk fashion. It may be a while before you can get the utility company to turn it back on. On the other hand, if you turn the gas off, it is indeed off.

The decision will vary with the circumstances. I would be just as aware of downed electric wires, among the many potential haards, as leaking gas.