The Purpose of Man

[Inziladun]

Originally Posted by alatar

Were the Eldar always meant to fade away - those that didn't burn out?

That might seem to have conflicting indications. In the Prophecy of the North, the fading is made to seem a consequence of the deeds of Fëanor and his followers.

'And those that endure in Middle-earth and come not to Mandos shall grow weary of the world as with a great burden, and shall wane, and become as shadows of regret before the Younger Race that cometh after.'

Silmarillion Of the Flight of the Noldor

However, Gandalf tells Aragorn his kingdom will encompass all he can see from high up Mt. Mindolluin, and

'...the time comes for the Dominion of Men, and the Elder Kindred shall fade or depart.

Return of the King The Steward and the King

He doesn't single out the Noldor for that fate. And earlier in the same book, while Legolas and Gimli talk in Minas Tirith, they discuss Men:

'It is ever so with the things that Men begin: there is a frost in Spring, or a blight in Summer, and they fail of their promise.'
'Yet seldom do they fail of their seed,' said Legolas. ' And that will lie in the dust and rot to spring up again in times and places unlooked-for. The deeds of Men will outlast us, Gimli.'

ROTK The Last Debate

Legolas, at least, appears to have the belief that not only Elves, but Dwarves as well, would 'fade'.

I would guess that the voluntary departure or inevitable fading of the Elves was indeed part of the plan from the start, or at least from the time when Men entered the Music. It seems to me that is bound up with the fundamental thing about the Elves that differs from other races: immortality. Why would their 'right' home be in Middle-earth, a quickly changing environment with constant death and rebirth? That just seems to be incompatible with their nature. In the Blessed Realm, without Morgoth to stir hatred and lies in them, the Elves are at peace.
As for the threats made to the Noldor in the Prophecy, maybe that can be reconciled as a promise that the Noldor would simply fade sooner because of their deeds, and the effects of Middle-earth would be swifter in bringing about the 'weariness' in them, as opposed to the Dark Elves and the Sindar.