So if there was no Facebook would another Facebook clone take it's place? Intuitive answer is yes, until you start thinking. How did Facebook got so big? It was best product on the market. So now Facebook is dead, what happened to Facebook? Is there a reason it died, if Facebook could not survive, how will it clones will not only survive, but thrive?
So here I would like to make a small prediction. The only way there will be another Facebook, if someone would make something better. Something which will either do things that Facebook does better - and hence kill it off, or something that will open entire new market.
TL:DR If you want to get big you can't be another Facebook: you either must be different or better.