To answer your question; No.
However, repowering the Hub will cause everything in the volatile memory to be list. As you observed when the Hub lost connection to the WeatherFlow servers, the data from the Air and Sky was stored in the Hub, then sent to WeatherFlow once the connection was restored.
I imagine the Hub established the connection before you rebooted the Hub. Had you disconnected power before the connection was restored all that data would have been lost.
You can learn more by reading this topic: