That means that once the endgame begins, you can’t go back into the game world. At a New Vegas demo last month, senior producer Jason Bergman told me that the ending to New Vegas “explains things well beyond the end of game,” including “what happens to every one of our factions and major characters.” That seems unlikely to happen with Fallout: New Vegas because of the way the game ends (and what the ending tells you). The main story quest of Fallout 3 (spoiler alert!) ended the game, but the “ Broken Steel” add-on changed the ending to let you go back into the Capital Wasteland.
