Uninstall ZAF application event

I am building a ZAF app that communicates with a backend. 

On installation, I want to call an external endpoint that makes my backend aware of the ZD instance. 

On un-installing the application, I want to call a different endpoint to tell my backend that this instance is no longer using the application. 

Registering the app will cause the backend to periodically poll an external system for each registered instance. If an instance removes the app, I want to ensure the backend isn't still doing that processing. 

I think I can accomplish the registration part by using the on_load event. But no idea how to handle removal of the app. 

Any suggestions? Thanks in advance.