Yep. Eventually, the entire current active population will either leave or return to the lurker stage.
If you left now and returned in two-three years, I doubt you'd recognize more then a dozen of the active members.
It's a natural process, as a whole.
If you look back to how the board shortly after it has been formed and compare with how it is today, you will see that it didn't stay the same.
The indispensible, fearsome and unstoppable... FORUM STAFF!!!
(just a light-hearted pun)