I think this line of reasoning depends on whether there are actual previous examples of 'gimmicks' the size of facebook evaporating in this manner. Without any research on the matter, I'm inclined to say Facebook is simply too large and to entrenched at this point to be a fad. It's qualitatively different from fads in the same arena that came before it.

But it's an honest question. If there are previous examples of facebook-like fads suddenly disappearing, the line of thinking is sound and possible.

I suppose email was a fad?

Fb has replaced all my personal communications

What makes you think facebook is a fad?

All the other similar fads before them.

Facebook has already remained vital and growing longer than the Friendster/MySpace precedents, and the Geocities/Angelfire precedents.

They're looking more like email or the web itself. Or the telephone.

Or did you have other 'similar fad' examples in mind?

Now that you mention it, email! Its going the way of the 1st-class stamp.