From personal experience, I can say that MyBlogGuest is earning visitors mostly from the word of mouth, so in that way we do heavily depend on social media (as an umbrella term for anything except search rankings). Google does drive us some good traffic, but 50% of search visitors come from the term "myblogguest", so they must have heard about us before searching.
So can I say I really depend on social media? I'd say, it's a different dependency than, say, from search engines. If search engine traffic disappears, we'll lose like 40% of newcomers. If Twitter bans our official Twitter account, we'll hardly see any impact on traffic.
Social media impact is not easy to measure, hence that's not an easy question for me!
Everything will be ok in the end
If it's not ok, it's not the end