Fallout 76: 10 Take-Aways From Bethesda's E3 Conference
6. The Plot
Todd Howard described the plot as a quest that the Vault 76 Overseer sends you on, although what exactly this plot is isn't definite (and will likely be ignored by the majority of players).
We already know about Reclaimation Day, and the drive to liberate the Wasteland from the monsters that were created by the dropping of the bombs. However there will likely be a more specific driving force than just booting the players out of the vault into a new world.
In describing the world, Howard explained that the quest will take players through six distinct regions, and it's likely that exploration will be part of the plot as well as part of the player's story.
Howard also didn't address how the story would work on a multiplayer-based game, although as a whole it seems a lot less focused on story than previous Fallout games.