Bloodmoon:Essential NPCs

The NPCs on this list are considered "Essential" by the game. If any of them are killed at any time, you will receive a message stating:

With this character's death, the thread of prophecy is severed. Restore a saved game to restore the weave of fate, or persist in the doomed world you have created.

This means that you will be unable to complete the Main Quest. A list of essential NPCs in Morrowind can be found here.

NPC	Location	When Essential
Captain Falx Carius	Fort Frostmoth, Carius' Chambers
Tharsten Heart-Fang	Skaal Village, The Greathall / Solstheim, Mortrag Glacier: Inner Ring