Uninstalling doesn't send a notification to signal.org, I've previously messaged a few people without getting a response, later realizing they never got it because they switched phones and stopped using Signal without pressing the "Delete Account" button in Signal settings. The workaround is to have the user install+register again, then press delete.

https://support.signal.org/hc/en-us/articles/360007061192-De...

> Signal must be actively working on your phone to make changes to the account. Register to see these options for your number. Deletion requests are not accepted outside of the registered app because there is no way to accurately verify whether or not a number is truly associated with the requester.

Yes, I expected as much: most users who stop using Signal (because, say, their friends use something else) are more likely to either just stop using it or uninstall the app, without explicitly deleting the account.

FCM system they use to deliver notifications will return the delivery ID as no longer valid after uninstall though.

I dunno. It's true they might not even have that information.