When the user clicks the Back button to exit the app, this can be captured using Keycodes in the Activity_KeyPress event.
When the user clicks the Switch/Choose Window(s) button, this can be captured in the Activity_Pause event.
If, after the Activity_Pause event fires upon switching windows, they come back to the app, then Activity_Resume fires.
But, is there a way to capture if they close/kill the app while switching windows (on my Android, this is done by clicking the Switch/Choose Window(s) button and, then, clicking the close-window X in the top-right corner of the window from the multiple windows shown)?