I don't think Lauda is gone.  I believe he's still around and has done a great job keeping his new identity from being discovered.  Even at the end it seemed to me that he loved this forum, and loved it too much to just give up.  The "goodbye" post was surprising only in the way that I should have expected it.

I think the "Lauda" account just got too burdensome with all the baggage.  Most people would find all that drama distracting, I know I would.  Maybe he just wanted to start fresh, without all the distractions.