I think it’s more important than ever to not rely overly on a single traffic source. For www.ancient.eu, our main source is Google, which is just as risky as relying on Facebook. Luckily, every change Google has made so far has benefited us.
Ideally, publishers should plan for individual sources of traffic going up or down. For example, at Ancient History Encyclopedia we’ve introduced a monthly membership: Our readers pay, whether they visit the website or not. This helps us bridge low-traffic months (summer holidays, for example), and it also gives us a good buffer if our traffic from any individual traffic source goes down.
Patreon is another very popular funding source, which is also independent from traffic. Definitely worth looking into for bloggers, podcasters, and other publishers who can build up a following.