I'm trying to execute some code whenever my activity is killed, but not when it's simply moved to the background (so just calling it in onPause() isn't a solution), and I understand onDestory() is not guaranteed to be called. I've been searching all over and haven't found a way to do this. How can I go about tackling this problem? Is it possible?
Nothing. You can never be guarantied to be called when an app ends, because it can always be terminated abnormally- it could crash, the battery could be pulled out, etc. onDestroy is the closest you can come. But you should never write a program that requires cleanup at termination time.