Of the products you listed, Youtube is the only one that I think is really orthogonal in the sense that it could bring in significant revenue if google's core product were disrupted. Perhaps maps and docs as well, to a much lesser extent. Gmail and chrome exist in competitive enough market spaces that I don't see them being able to stand on their own at all.
It's the familiar old adage about backup systems: interdependencies lead to concerted failures. A nuclear reactor with 500 backup systems that all depend on having a stable electrical supply isn't safe at all.