Simple math
I answered a similiar question in a similiar forum in a similiar way: Forget about the stupid button.
The only thing that button does is calculate the closest airport.
What you really want to know (and should have already calculated in your head) is: Where is the high terrain and what direction should I turn when the engine stop turning?
I flew single engine airplanes IFR over mountains and large bodies of water in Alaska. I constantly asked myself: If the engine stopped turning right now which direction would I turn?
It's a constant process.
You cannot simply drive along unconscious of your environment and then when everything heads south, just punch a button that magically saves the day.
It's just not that simple.
Fly the airplane.
Good luck.