When someone leaves FB, he makes a public declaration. But his return years or months later is generally silent.
Not claiming everyone that leaves FB, returns. But Facebook is continuing to expand.
I remember reading here years back that new generation isn't really using FB cause their parents are using it. And they weren't comfortable with that setup. Rather they are switching to other social media.
Well, it at least called itself "Earth's Biggest Bookstore" at that time.