This mod is OUTDATED. But the guidelines in the description might be useful.

Attention:
If you don't want to use this mod for the rest of the game, create a new save file. There are a handful of quests that if you start them while this mod is active, NPCs involved in those quests will lose their essentiallity for the duration of those quests. (only in those quests)


This mod removes the essential, invulnerable and ghost flags from every NPC (including children) so that they can be killed by
you or anything else (like dragons & falling damage).
Even NPC's [actors & dragons] that become essential in a certain quest are covered up, and it doesn’t have ANY requirements.
[No skyrim.ini modifications are required]

GREATLY increases the role-playing factor.
In the Vanilla game, if you attack someone, they usually won't talk to you again & will attack you on sight in the future.
Also it is logical that if someone's dead, they can't give you any quests!


It WON'T BREAKE a quest line (because of a dead NPC that is important to the main quest or has a vital role in a quest),
IF you read the bottom of this description.
If you're not comfortable with some of your followers being none-essential (like Delphine who gives you quest objectives later),
you can use the 'Ultimate follower Overhaul' mod to make any follower an essential NPC (on-the-fly).
Or you can use the command line


Definition:
Essential: An NPC that can’t be killed and if its health goes down it will just crawl around until its health regenerates.
Invulnerable: An NPC that doesn’t take any damage & doesn’t bleed!
Ghost: An NPC that can harm you, but you can’t harm him/her.
Protected: When the actor's health reaches zero, s/he falls to the ground & his/her health starts regenerating. But if you
attach him/her again, s/he will die (usually applied to followers). This mod doesn't change this flag.


Tested with Skyrim 1.5.26 & 1.6, but should work with any version.

I checked the compatibility with:
Script Dragon
SKSE
Live Another Life
True Giants
Ultimate Follower Overhaul
Populated Cities
Dynamic Merchants
.
.
.
And many other mods

This mod should be compatible with almost any mod (assuming it's the last item on your load order!).


If you see someone who is still essential, it is because of another mod [that is lower on your load order] or because you've
already started a quest (you used this mod in the middle of your game) & their status is saved in your save file (RARELY happens).
OR because another mod made them essential on-the-fly. Like UFO, which does so by your choice (for your followers).
(Not applicable if you add those optional lines to skyrim.ini)



* INSTALLATION *
1-Use NMM (Nexus Manager) & follow the on screen instructions
OR
2-Manually:
-Just copy everything from Data folder to the Data folder in your Skyrim installation directory.
*****
After a quest starts, the essentiality flags that have been changed by that quest, remain in your save file for the rest of the quest.
If you don't want to use this mod for the rest of the game, create a new save file or use the Safe Version.
[If you're using the safe version, modifying the skyrim.ini is HIGHLY recommended.]
*****
-If you don't want the dead bodies to clean up,
copy WIDeadBodyCleanupScript.pex in optional\No Cleanup\scripts to Data\scripts\ folder to your Skyrim installation directory.
The script works regardless of the respawn times & does not make any change to them.

-If you want to increase the respawn time, to prevent new NPCs from spawning & prevent creating piles of bodies,
copy ONE OF THE FILES in optional\Increase Respawn Time to the Skyrim\Data directory.
By default in the vanilla game,NPCs, Creatures & Items in Normal Areas respawn after 10 Days or 240 Hours.
Areas that are marked cleared on your map respawn after 30 days or 720 hours.

-Activate the esp files with the mod manager of your choice.
For the best effect, put it at the bottom of your load order.


3-OPTIONAL STEP:
Since some NPCs become essential as part of some of the quests, to make sure that everyone can be killed you can add these lines to skyrim.ini (located at "Documents\My Games\Skyrim").
[I tried to cover those quests, but I might have missed some of them. Although I haven't encountered any scenarios like this.]
With this change you can kill essential NPCs added by other mods too.

[GamePlay]
bEssentialTakeNoDamage=0



-----------------


* UNINSTALLATION *
If you installed it using NMM, then just deactivate or delete it.
Or
You can manually remove the following files from the Skyrim’s installation directory:
Data\Kill Every NPC.esp
Data\scripts\QF_DialogueMarkarthIntroWorld_000AF75F.pex
Data\scripts\WIDeadBodyCleanupScript.pex
Data\Skyrim x Day Respawn.esp


=============================================================

ATTN:
IF SOMEONE HAS BEEN KILLED ACCIDENTLY
by something or someone
Or you can't find an NPC in his/her usual place [and you think they might be dead!!!]
(Many thing happen around you when you're in a cell)



Do these steps:

1- Select their corpse by clicking on it or with "prid" command:


4- Type "resurrect 1" (without the quotes) & press enter.

5- If that NPC is hostile towards you (because you killed them!), [while you have them selected] just type:
resetai
And press Enter.

=============================================================

Sometimes the game might clear the dead from a cell after a while [after passing the respawn time] or because of the
excessive dead (if you don’t install the cleanup script).

In these cases the corpse [of some of the important actors] will be teleported to another cell named "WIDeadBodyCleanupCell".
To teleport to this cell (& to make sure that they're there :) ), type:
coc WIDeadBodyCleanupCell

To teleport back to where ever you were use "coc <cell ID>" command, to teleport to a nearby cell & then fast travel there.
For example:
coc whiterun
Or
coc riverwood
Or
coc riftenorigin

Then type:
player.placeatme <base ID>

This command places another copy of the NPC (just like the old one :D) next to you.

To find the "base ID" just open the console and type:
help <NPC name> 4

For example to find Sven's ID, type "help sven 4".
You can scroll the list using the Page up/down keys.

You’ll find his ID in a line like this:
NPC_: (0001347F) 'Sven'

'0001347F' is his ID.


For example:
player.placeatme 0001347F



*Note:
To make any NPC (including those added by other mods) Non-essential use the command:
setessential <base ID> 0

to make any NPC, essential, just replace 0 with 1
[This change is saved in your save file.]

=============================================================

* CHANGE LOG *
V1.2
- Added a safe version that doesn't cover the quests
- Minor changes to the NMM installer
V1.1
- Compatibility with patch 1.6
v1.0
- Initial Release

Special thanks to:
miongbesar - It's basically her mod but without the side effects & some of the
incompatibility issues, with updated quests & NPCs [as of patch 1.6]. Plus the compatibility with NMM & modularity.
All credit goes to her.
Bethesda
darkOne