Looking deep into the datasheet there is a graph shown on page 6 called "Operating Quiescent Current" that shows a minimum current consumption from about 15 to 22ma depending on device temperature. This would be like having a LED as a only load on a battery and would of course discharge it in a calculated time frame based on the mAH capacity of the battery. If you had a 9vdc battery rated at 150mAH the standby current of the regulator would probably discharge the battery in 10 hour or less time frame.
However this chip appears to have a nice extra feature called external shutdown on pin 5.
ON /OFF — Allows the switching regulator circuit to be shut
down using logic level signals thus dropping the total input
supply current to approximately 80 µA. Pulling this pin below
a threshold voltage of approximately 1.3V turns the regulator
on, and pulling this pin above 1.3V (up to a maximum of 25V)
shuts the regulator down. If this shutdown feature is not
needed, the ON /OFF pin can be wired to the ground pin or
it can be left open, in either case the regulator will be in the
ON condition.
This 80ua minimum current consumption when forced to off, would probably not drain a battery much more then it's shelf self-discharge rate and is the feature you should utilize if you wish to extend standby time for applications that only run for short duration and are then shutdown.
Lefty