I was just doing some testing on mobile nostr clients and it seems some don’t delete the npriv when the app is deleted. Please fix this if your client has this issue. @primal is one example. 

 Android or IOS?
On Android uninstalling an app should remove all the associated data. 

 iOS 

 I suppose it is an idea to offer a better “UX” if the user reinstall the app, which can become really risky.