Rofl I don't think that would keep it safe. I remember reading about a celebrity that "accidentally" put nudes on Instagram, then realising what she had done removed them a few seconds later. Too late, they had already been downloaded & archived by hundreds of people. With search engines like Google caching everything, stuff tends to stick for a little while too.
As for Facebook, I really do think it's too big to fail at this stage. People may get bored of it, but there is an ever increasing internet populace to keep up numbers. It's kind of like Google, Youtube, Ebay, all these sites are too big to fail & know too much about you for you to leave. Youtube especially just has too much content it will never ever disappear.