I just ran this quest twice in a row with one other person in the group. First time, avoiding all the ambushes by pathing the NPC through the woods off the road. He disappeared on a branch sticking out of the ground on the western side of the road around coordinates 29:15 shortly after entering Ashenvale. Quest did not fail, but the NPC was completely gone. We abandoned the quest and ran all the way back to start it over. This time, following the road and dealing with all the ambushes, twilight cultists and furbolgs and all that. We went super slow after entering Ashenvale and still he disappeared in exactly the same spot, on the same branch.