Arwen's Mortality

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The whole point of the choice is that it is irrevocable. Elros was a Peredhil who chose to live as a mortal, albeit with a much extended life-span. Elrond chose to be among the immortal. The choice was then only extended into Elronds family. Why; because to choose the mortal path meant death in ME, to choose the immortal meant that at some point in time your life would continue in Aman, whether there was a time limit on your arrival in Aman is mere conjecture. The decision to become mortal is akin to the choice of Luthien; who chose to live a second life as a mortal and to die indeed, leaving the circles of the world forever.