Don't know why this is so downvoted much. Just because Facebook evaporates doesn't mean the very concept of "social graph" will go down altogether with it.

Facebook will probably be replaced with more flexible identity and social graph architecture that's more decentralized.

It's different from McDonald's because humans have to eat, and McDonald's can always pivot or acquire other companies to provide the type of food that's more in vogue, but what Facebook has created is equivalent to a nightclub. When a nightclub loses its reputation it's very hard to recover.