[Belegorn]

I believe the Elvish fading is a byproduct of Melkor's influence on Arda. That's why I brought it up and because it kind of reminds of of the Nazgûl. Their bodies apparently were not supposed to do that but somehow through some taint perhaps it cannot abide the soul of an Elf for so long. I think in this condition they actually became literally invincible, like unkillable by any means they used to get killed by. Not quite the same with the Nazgûl.