And they must have known it was imminent, it seems unlikely they had a drone over it 24/7 given the available hover time.
PS: Apparently I'm not alone with this idea, search engine comes up with hits. https://elistair.com/ even have a tether kit you can plug into some DJI models (and others) instead of the conventional battery pack. Out of Lyon, France, nice!
https://www.nsf.gov/news/news_summ.jsp?cntn_id=301674&org=NS...