macOS System Preference Pane and applicationWillTerminateNotification

Im thinking of building a System Preference Pane, but are wondering if it will receive the applicationWillTerminateNotification from another app, even when System Preferences has not been opened.

essentially what i want to happen is:
-some application is closes.
-notification is posted, and something else happens.

how would i do this?
would I have to make some kind of helper app, that is launched at System login, so as to receive the notification.

im just not sure.....

can anyone shed some light on this.

thanks in advance