Please refer to applicationWillTerminate
By Apple documentation it says:
This method lets your app know that it is about to be terminated and
purged from memory entirely. You should use this method to perform any
final clean-up tasks for your app, such as freeing shared resources,
saving user data, and invalidating timers. Your implementation of this
method has approximately five seconds to perform any tasks and return.
If the method does not return before time expires, the system may kill
the process altogether. For apps that do not support background
execution or are linked against iOS 3.x or earlier, this method is
always called when the user quits the app. For apps that support
background execution, this method is generally not called when the
user quits the app because the app simply moves to the background in
that case. However, this method may be called in situations where the
app is running in the background (not suspended) and the system needs
to terminate it for some reason. After calling this method, the app
also posts a UIApplicationWillTerminate notification to give
interested objects a chance to respond to the transition.
If you want to have user's location when app is not in memory, short answer: Impossible.