In my opinion that is highly unlikely.

For one thing, myspace was largely a network of early adopters. Therefore it was not a surprise these people would look for something new soon.

For another thing, "everyone" is on facebook and thus it is not convenient to leave. Most people don't like change after all. We all know how long people stuck with IE6 (and that was just a browser).

I'd say we have 2+ decades of FB ahead of us.

We'll need a replacement for all the pleebs to use.

I fear any replacement will be just as bad.

Use Diaspora.