Doesn’t sound like retaliation to me, it sounds like their scheduled web crawlers are finding that content they used to index is now no longer viewable and this removed from search results. Pretty standard. My guess is that there were 400 million URLs listed and as the crawler uncovers that they are no longer available, that number will keep dropping to reflect only content publicly viewable. If only 500 URLs are now publicly viewable (without logins) then that’s what they will index. Google isn’t a search engine for private companies (unless you pay for the service) they are a public search engine so they make an effort to ensure that only public information is indexed. Some folk game the system (like the old expertsexchange.com) but sooner or later google drops the hammer.