Glorifindel says to Earnur of the Witch King:
“Do not pursue him! He will not return to this land. Far off yet is his doom, and not by the of hand man will he fall.”
From Lord of the Rings/The Battle of the Pelennor Fields:
Merry’s sword had stabbed him from behind, shearing through the black mantle and passing up beneath the hauberk had pierced the sinew behind his mighty knee.
So passed the sword of the Barrow-downs, work of Westernasse. But glad would he have been to know its fate who wrought it slowly long ago in the North-kingdom when the Dunedain were young and chief among their foes was the dread realm of Angmar and its sorcerer king. No other blade, not though mightier hands wielded it, would have delt that foe a wound so bitter, cleaving the undead flesh, breaking the spell that knit his unseen sinews to his will.
During our last class discussion in Bilbos-study, we had quite a bit of discussion about the role of the Barrow-downs blade in the death of the Witch-king. Who or what really killed the Witch-king?
Was the spell of the Ring broken by the blade making him vulnerable to the sword?