[The Squatter of Amon Rûdh]

The letter alluded to above is #153 (September 1954), which is a draft. In it Tolkien says

[Elrond's] children - with a renewed Elvish strain, since their mother was Celebrían dtr. of Galadriel - have to make their choices... The end of his sons, Elladan and Elrohir, is not told: they delay their choice, and remain for a while.

I think that the dating of this letter at a time when the appendices were still unpublished and its status as an unsent draft should make us cautious about accepting what it has to say without question. It does seem to confirm, though, that physically going with Elrond or remaining behind did not constitute a choice. The decision would seem to be a moral one that was permanently binding once made, but which could be postponed albeit not indefinitely. However, as Findegil pointed out, and as the title of my last post here implies, this makes very little appreciable difference to the choice itself and leaves me admitting freely to the shameless splitting of hairs. Like Elrond and Elros, Arwen, Elladan and Elrohir are choosing the fate of one race or the other. I do think, though, that the wording of this letter implies an imminent deadline. I doubt that the decision could be postponed for very long.