Obsidian Entertainment are skipping the easier way of creating a branching RPG experience with The Outer Worlds as they have decided not to introduce essential NPCs that are unkillable. If you feel like it, you can murder everyone.
The Outer Worlds is the game singleplayer RPG fans are looking forward to in 2019, as it will have the features Bethesda and BioWare abandoned in favour of the games as a service model. As a cherry on top, it appears that Obsidian decided to get rid of one major annoyance that was latched onto all of BioWare and Bethesda games - the unkillable NPCs.
BioWare games straight up prevented players from pulling out weapons in some areas, essentially making the NPCs impervious to your wish to kill them, while Bethesda simply went the lazy way by making some NPCs essential. In other words, this meant you could impale, slash, burn or slam annoying people such as Maven Black-Briar or her sons, and they would still wake up a few moments later and proceed as if nothing ever happened.
This major immersion breaker will not be present in The Outer Worlds, as Obsidian's senior narrative designer, Megan Starks, stated that the developers "have a philosophy where [they] feel like it makes for a better gameplay experience" to allow players to simply wreck any NPCs they feel like.
Therefore, it is inevitable that some players will kill NPCs that are crucial for The Outer Worlds' story. This wouldn't be much of an issue in a linear game where an NPC's role would be minor and the story could progress without it, but when there is a world populated with different NPCs, each of whom have a specific agenda that can alter the game's ending, such a decision has major consequences.
For example, killing the scientist that is shown to free the player in The Outer Worlds announcement trailer will likely lead players down another path where they can side with a different faction and proceed to complete the game. Killing their characters would mean players need to progress the story somewhere else, creating the need for a large number of different endings.
There is currently no official confirmation from Obsidian on how they plan to deal with this, and some fans have already started asking questions about what might happen if they were to kill all the NPCs in the game. It is possible they might pull a similar stunt as in Fallout New Vegas, where Yes Man was the only essential NPC that would prevent players from halting the entire story's development.