[blackflame7000]

I think you missed the point because it's irrelevant if Telephony has the capability. MQTT does not and there is no way to send a message once disconnected (Telephony included). The best you can do is preemptively say, "Do X if I get disconnected". X could be "Reconnect if not intentional" but if it was a network issue, you might perceive the lack of reconnects as an intentional hangup when really its network issues. Going back to the OP, MQTT has no way to distinguish intentional vs unintentional disconnects from the client(subscriber) prespective.