Original 'Navigator' script's ending was much better:
In the final cut, the kid insists to Max that he wants to take the chance at traveling back to 1978, there's that trippy time travel/lightning scene, he wakes up in the forest, and then when he gets home he sees his 1978 family waiting for him, happy ending, etc.
It's a little known fact that this was a last minute reshot tacked-on ending after preview screenings of the original ending were unenthusiastic. As originally shot, Max and David go back in time, time travel/lightning scene, David wakes up in the forest, and starts walking. He's going through the woods happily, thinking he's made it back to his own time, when he hears a noise in some bushes. Thinking it's his younger brother trying to scare him again, David goes towards the noise, only to come face to face with a band of filthy grunting Neanderthals. Screaming incoherently, they viciously stab him to death with sharpened sticks and then take turns sodomizing his mangled corpse. The last shot of the movie is Max hovering over this scene saying, "Oops, went back too far!"