(spoiler)
Well, you may want to play the other routes to understand it better.
Flynn's route ends with him becoming the the monster! The picture shows whats left of his body after burning in the mine and traveling through time! The little kid in the picture is Jenna. She talks about seeing the monster in another route. As for Chase and the others, their not shown. I assumed they survived Echo maybe with some mental trauma and morn the death of Flynn. Carl and Dax saw Flynn burning in the mine, they would tell the others he's dead I guess.