We Happy Few has seen many changes as the game's budget increased and the developer studio, Compulsion Games, got bought out. Sam Abbott, the game's producer, talked about the game's length and different modes before the official release.
Abbott's new information came from an interview he did with GameInformer, where he talked about the massive changes that the game has undergone over the years, as well as its length and sandbox mode.
We Happy Few was originally a "highly repeatable 1-hour game" but this has changed during the game's stay in Early Access, as it is now a 20 hour experience according to Abbott. The replayability will still be there though, so you won't just go through 20 hours of gameplay and then toss it way.
The game has also shifted its focus to narrative, and away from the survival elements. Abbott stated that Compulsion Games received a lot of feedback from players early on and many of them claimed they didn't like the survival element. Therefore, We Happy Few slowly shifted its form from the previously mentioned one hour replayable game to a 20 hour story-focused one.
As mentioned, the replayability will not go away either and the planned sandbox mode will also serve that purpose. Unlike the story mode, this one will focus on survival, procedural generation and many replays. According to Abbott, this is due to their wish to go back to the game's roots in order to cater to the players who initially liked it as well, so they are not left out either.
He has also stated that procedural generation was the easier way out for the studio, as they are not a huge one with unlimited manpower. Having handcrafted maps would mean they would have to opt out for smaller areas, which in turn wouldn't feel like a city.
That said, the sandbox mode will not be available at launch, on 10 August 2018, as Abbott has confirmed it will come later on in the form of post launch content. You can check the interview for more insight on the game's road to release as well as Abbot's thoughts on them.