This shows a single check mark, no? Ie it tells you that the user hasn't received the message.
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.
You don't have to figure out if the user uninstalled. This also happens if they get a new phone and don't re-install on it, so relying on uninstalls wouldn't work anyway.