I would say fair, considering where the short story left off it could have gone in either direction. With them making it to safety, or with the scenario that happened in the movie. I actually was impressed the movie decided to end it that way (did any of you notice the woman from the beginning who left for her two children was safely on the truck? I didn't notice until my second watch-through. She actually plays Carol in The Walking Dead, great actress!). Not enough movies, or stories for that matter, end with a negative ending. I think it has become universal to expect a happy ending, but sometimes reality hits you that much harder. It IS a plausible scenario, and in his mind he was only trying to do right by the people he cared for. One of the best movie endings I have seen in a long, long time. Nothing prepares you for those screams at the end, it chills you straight through.