I would be more worried about Northern Virginia. I doubt the world at large would notice much problem if SFBA dropped off the network, but they sure would if the same happened to NoVA.

AFAIK till quite recently, if not still, us-east-1 was SPOF for various components of AWS. Your already deployed things would continue to work, but APIs (and most importantly, Console) wouldn't, IIRC.

A typical multinational social media operator has datacenters around the globe. The question is rather whether these can really function independently should the central ones go offline.