It totally sucks that this happens, when you are doing your best to provide a great wealth of information for people. But it is the same thing that has been happening to so many website owners for the past two decades or more. I remember reading posts that were not too dissimilar to yours today, back when Google would make changes in the early 2000s. I am sure you already know, but it just comes down to loving the traffic from Google, but not being dependant on it and having other avenues for readers to find you.