+1 for this feature!
Thanks, Alex. This has happened to me in usability tests also.
It would be really nice to add a Settings item to the Axure App menu. The Settings sub-menu could have options for Exit, like Triple-Tap, Triple-Tap In A Corner, Swipe From Edge, Swipe Up With Two Fingers, Pinch, Shake, etc. Multitouch and motion detection are good options because Axure doesn’t support them in prototypes (but hopefully yes in future? Pretty please?) There should also be an option for No Exit (user would have to exit app, then on relaunching app with this setting the app home screen would load instead of the prototype) ...etc. Also options for Refresh Current Page and Reset Prototype.