Hope for Undomiel.

[Legolas]

To answer the first question with a quote which I (intended to, but) failed to give:

The view is that the Half-elven have a power of (irrevocable) choice, which may be delayed but not permanently, which kin's fate they will share.

Here Tolkien says it was irrevocable. Irrevocable is defined as incapable of being recalled or revoked; unchangeable; irreversible; unalterable; as, an irrevocable promise or decree; irrevocable fate.

Tinuviel: That is a common misconception. Elrond is descended from both men and elves, and his family is known as 'half-elven' because of that.

Prior to his parents, Earendil and Elwing, anyone with any mortal blood was considered mortal and would die as a man would. With Earendil and Elwing's accomplishments, they (along with their sons) were granted the choice of mortality or immortality.

Elrond chose immortality, of course, and he married an elf - Galadriel's daughter - who gave birth to Arwen. Arwen was thus half-elven too because of Elrond's portion of mortal blood. She was a half-elf - not an elf. When she made her decision, she picked mortality. She was never immortal - it was just decided that she would age like the Eldar did until she decided which fate she would suffer.

Tolkien explicitly states that half-elves are not the same as elves in Letter No. 345:

Arwen was not an elf, but one of the half-elven who abandoned her elvish rights.

[ March 29, 2003: Message edited by: Legolas ]