John disappeared a while back.
First, it was thought that he was in an accident, or that there was "foul play" of some kind.
Later it turned out, that apparently he decided to leave on his own accord.
As to the reasons why, that's anybody's guess..

Some info here: http://www.rcgroups.com/forums/showt...light=Derstine

and here : http://www.rcgroups.com/forums/showt...light=Derstine