See, if this thread was about quests offering more paths and options, where NPCs that would otherwise be essential would be trivial in an overall narrative, I would be right up there with everyone else arguing for more diverse quests. I would give a lot for more quests like Birds of a Feather and Heartache by the Number. Cass was a beautiful example of how many alternatives there were for solving her dilemma. You could turn her over to the Van Graffs in Birds of a Feather, or you could tell them to [censored] off in the form of a .45 acp in Heartache by the Number.
It didn't bother me one bit that Birds of a Feather failed because the game was able to accommodate the situation where it failed, and this was largely due to a player's decision to participate in a quest that has cross-over with the former. I want more quests and more narratives that support these circumstances.
In the grand scheme of things we can all agree that it's a videogame not set within the harsh reality that is real life. The main ideal is finding a solution that is not only possible within the limitations of the game's narrative, but also in the technical aspect of the game.
It's possible to have a living, breathing world because it doesn't take much outside of scripting/packaging to make an NPC wander around the backyard of his home and toil the fields. This same NPC can also die because they don't serve an overall story or narrative. They're filler much like the numerous caravans of the Mojave. But, the NPC doesn't have to serve an overall narrative to be more important than the generic NPC that might replace him/her should they die. The various personalities that populate these worlds are important in that they provide life and believability beyond just the mundane tasks they do every single day. When they die, a bit of the life they once breathed into the world goes with them.
In a game like FNV, this isn't so much of an issue because the NPCs exist within their own insulated cell, and so it was entirely up to the player whether these NPCs lived or died. In fact, the game made numerous accommodations and options to support an NPC dying. No matter what though, any NPC that did die in FNV was always, in one way or another, the result of a personal decision made by the player. Contrast the that to Skyrim and you have NPCs that wander beyond home and into the great beyond. I don't want the very few NPCs that already exist, who provide life to the world, to perish as a result of a random occurrence that the player had no control over.
I don't feel it's fair to say it's self-contradictory to want a believable, realistic world environment that also doesn't harbor the same consequences of real life. It's fair in this situation to find a gray-area to an otherwise black and white issue. In a game world that doesn't facilitate or accommodate certain consequences, a sacrifice to realism and believability has to be made in order to keep a consistent and intuitive game experience.
Trust me, I dislike essential NPCs as much as the next person, but I can shelve my disdain for it because I understand why it exists. With that said, the essential system can be eliminated completely and replaced by a system like an improved 'protection' system. One that can identify when the player is actively trying to kill an NPC vs trying to protect an NPC.