It should be said that this kind of thing has always been possible through the use of mods. Redditor menschletzt figured out a way to get around this though. Though first appearing in Oblivion to mixed reception, the feature was carried over into Skyrim where it continues to save careless players and frustrate players that just couldn't care less. In an effort to protect the player from themselves, Bethesda introduced Essential NPCs, characters in the game that cannot die under any circumstances.
While many enjoyed this freedom, it did come with a consequence that players could potentially lock themselves out of certain questlines, including main story missions. In the old days of The Elder Scrolls, back in Morrowind, players were permitted to kill any NPC that they could reach.
