Q:

Apple APNS stream with unregistered devices

I couldn't find any decisive answer in Apple's developers area regarding to an issue with unregistered device from APNS.
Assuming a device has unregistered itself from the APSN service, will I get any response in the stream about it unregistered, or the only way I can know about it is the use of Feedback service?
If in fact the feedback service is the only solution, what way is suggested to handle this success -> failure status?
To be more clear, if I don't get any response in the stream, it means it 'might' (use of Apple) reached its destination but then, the feedback indicates it was a failure.

A:

If a device unregistered itself from APNS via your code (i.e. your app's code initiated the un-registration), your app can notify your server to delete the device token (the same way it notifies the server to store the token after registration).
Otherwise, the only way for the server to know that a device token is no longer relevant (due to app being uninstalled from the device or the user disabling push notifications for the app) is by getting the device token in the Feedback Service.
As for responses in the stream, you only get error responses if the message is invalid. It can be invalid due to an invalid token, but an invalid token is a token that was never valid in the current push env (unlike tokens returned in the Feedback Service, which used to be valid, and may be valid again if the app is re-installed). 

To be more clear, if I dont get any response in the stream, it means it 'might' (use of Apple) reached its destination but then, the feedback indicates it was a failure.

If Apple didn't send any response in the stream, it means the message is valid, and Apple will try to deliver it to the device. If, when Apple tries to deliver the message, they discover the app was uninstalled from the device, the next call to the Feedback Service would return the device token of that device.

