Arwen's Mortality

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One thing i also think that Peter Jackson mis interpreted, or didn't accentuate enough concerning Arwen is that she made the choice to become mortal to her fathers heavy disgreement! In the movies he implied that she would die and that was somehow connected to the ring, and i agree with your description / analysis of the situation Legolas.
In the books Elronds' aggreivance with Arwens choice is more pronounced;

None saw her last meeting with Elrond her father, for they went up into the hills and there spoke long together, and bitter was their parting that should endure beyond the ends of the world.

Perhaps this situation was less "filmable" to Jacksons version, but it certainly has much more effect. In my opinion Jacksons interpretation even undermines the connection between Luthien Tinuviel and Arwen Undomiel, of who's 'likeness' she indeed walked, and who she shared the doom of mortality with. (That all should have been in the movies discussions... sorry)
But yes... the choice to become mortal was only ever given to the 'Peredhil' (a term i believe was only ever applied to Elros and Elrond) but means half-elven therefore includes Dior etc etc etc, although no-one else seemed to 'make' the choice except Elros, Elrond and Elronds children.
This means that when the choice is not conciously made the decendant of Immortal and Mortal appears to automatically be Immortal? As a result; Arwens death (and the inability of the other half-elven to have children with a mortal as they are no longer in ME) signifies the end of the half-elven in middle-earth! Although the most noble blood line to ever exist continues still in both Middle-Earth and Aman!