Fallout 76 may be built on the mechanical foundation of other chapters in the series, but its concept is certainly different, with an online focus. Some may be hoping that ultimately there'll be an offline version, but Bethesda now confirms that this won't be the case.
In a response to an inquiring fan on Twitter Pete Hines has confirmed that the game would have to be completely re-engineered in order to support offline play.
"it's a server based game. I don't see us completely re-engineering it to somehow be an offline game that is entirely client based."
Singleplayer servers will arrive, however, at some point after launch.