Hello
I have probably a dumb question but if I configure the availability topic of an entity via HA Discovery, how could the device publish the state “offline” if it’s indeed offline 
?
Thanks
It published that state just as it went offline.
Ok, so the device has to do a clean shutdown. In the event of a power outage the offline feature won’t work.
Usually in event of power outage nothing works. If its an individual socket unplug whatever your device is and report back what happens.
Look at last will and birth message for esphome
Right 
Thank you for the answers.