spoiler...
lofty idealism can sometimes get in the way you know? the movie suggests he was doing fine, all set to leave the wilderness and return to civilization, and he went back to cross what was once not more than a stream, but had become a torrential river which he could no longer cross. he then returns to his magic bus in the wilderness,seems to eat the wrong berries, thus gets poisoned, and dies.
It is a weird thing to say, but his death is presented in a very 'honest' fashion, for lack of a better word. i.e. he is not presented as a martyr, but you also don't feel like "what were you thinking, stupid idiot!" - at least I didn't. his death at the end is merely the end of the movie, most of the movie, I think, is actually more of a celebration of his life.