[Mithalwen]

I would have thought that Arwen's choice became final on her marriage. anything else makes a mockery and a nonsense of the pain of her choice for Elrond and her kindred. Had she been able to marry Aragorn AND remain accounted amongst the Eldar, Elrond would have surely waited for Aragorn's death before leaving - given his lifespan it would have been the equivalent of a mortal delaying about a year and a half (yes I have done the sums, sad bean counter that I am). For Arwen not to share Aragorn's mortality seems completely alien to Tolkien's concept of marriage or at least these idealised unions..

I am sure that Arwen did not age in body and thus her fate must have seemed all the harder - it takes bodily distress beyond hope of healing for most of us to contemplate death, as a gift. I think she died of grief.

The slight thorn in this issue is that of Mithrellas. Presumably she abandoned her family because she could not bear to see them age and die - although it says she was taken to wife by Imrazor, I don't think this means it was against her will.

As for Elladan, Elrohir (and indeed Celeborn), I guess they were on some mopping up detail and despite thier close association with the Dunedain I think they probably passed West for the reasons outlined by Ibri.