If the phone continues to work. Mine won't. Pretty much out of luck if the battery gets cold or the trip is more than ten hours.

I meant the data connection you get with a cell tower. Most apps on mine do not. The gps app i have does but the rest, forget it.

And of course, the hiker would have to leave info that they are using the app and there will be minimal chance of it. We could not get a reporting party to remember which trailhead they dropped off the group at. But, that will always be a problem regardless. 99% of all search subjects don't believe they will ever need rescue.