I noticed that a lot of Dragon attacks and other animals attacks happen on the weirdest places. And this could cost some of the NPC's their lives. Which i find quite annoying, considering i try to keep everyone i can possibly keep alive, alive. People that were killed in my game:

Captain Lonely-Gale – Windhelm – Dragon
Ghorza gra-Bagol – Understone Keep – Guards
Lod, Mathies – Falkreath – Spawned dead
Seren – Dawnstar – Dragon
Ranmir - Winterhold – Magic Anomaly
Aeri, Leifur – Anga’s Mill – Hagraven
Odfel – Shor’s Stone/Redbelly Mine – Frostbite Spiders
Alvor, Orgnar - Riverwood – Accidently killed by myself when I played the game for the first time.
Meeko – Meeko’s Shack – Accidently killed when he was a follower.

Captain Lonely-Gale and Seren were killed by dragons, just because they were stupid enough to attack a dragon with their daggers. I tried to kill the dragons as fast as possible, but they were still killed in the process.

Lod, Mathies, Ghorza gra-Bagol and Odfel are killed because of bugs. Lod and Mathies spawned dead. Ghorza was killed by the guards when she caught me pickpocketing her, and Odfel was killed by respawning spiders inside Redbelly Mine, which should not respawn.

Ranmir and Aeri and Leifur were killed by animals during certain quests. I didn't have a save from before taking the quest. And every time i reloaded the save, i couldn't slay the beast quickly enough for them to stay alive. Ranmir was killed by Magic Anomalies during the quest Containment. Aeri and Leifur were killed by a Hagraven during a companion quest.

I accidently killed Alvor and Orgnar in the beginning when i first started playing Skyrim. I didn't know much back then, including i didn't know i could reload or that they wouldn't respawn, and by the time i knew that, i hadn't have a same from before i killed them. They attacked me after i accidently killed a chicken and didn't know how to put my weapon away. I regretted it ever since. I accidently killed Meeko when he was my follower. It was dark, and i was attacked by a group of wolves, and he looked like a wolf in between a lot of wolves.

Today, a Frost Troll spawned in the Skaal Village, and attacked the villagers. I'm really glad to see that the villagers are essential and were only knocked down by the Frost Troll. Then i wished the characters i tried to protect, but were killed in the main game, were essential and that i could have saved them. Can't you implement i way for the characters to come back to life after a set of time, or after doing something? Two of the characters were involved in becoming thane of falkreath, three were vendors, and one was a trainer. One was a marriage option and one was a follower. I regret that these people are all dead. Please give me a way to bring them back to life.