MQTT-Google Cloud pub sub connection status

Question

Please help!

So, I have a couple of microproccessors and microcontrollers connected to the Google Cloud IOT Core running on the Mongoose OS. Now, I need to connect to the Cloud Firestore and need its connection to be updated on my device connection status.
But the event reporting the connection status of my mqtt broker to pub/sub is nowhere to be found. So, I never know if my device becomes offline or is online. I need to detect the connection to the firestore and know if its connected or disconnected.

Any hint on how to do it is much appreciated. Thank you.