[stanfordkid]

I think there is a different way of looking at it: how replaceable is he and what he has built?

The truth is -- most of Facebook's value comes from network effects, not the actual technology itself. If Mark Zuckerberg never existed, it is highly likely some other platform would have been created -- the knowledge and skillset he has is not that rare. many other platforms existed before Facebook to let you post pictures and chat with friends.