Arwen's Mortality

[A_Brandybuck]

I've also been thinking about this difficulty of the 'renewed elvish strain'. Macalaure's explanation may fit well (and is well, too), but could that be? Every child of an "Elvish-Half-Elven" is mortal?
I don't think so.

Tolkien marks the choice is irrevocable (Letter #153). That sounds like the choice is binding in all ways. Another point is the following quote also from Letter #153:

Elros chose to be a King and 'longaevus' but mortal, so all his descendants are mortal, and of a specially noble race, but with dwindling longevity

Here Tolkien pointed out, that the descendants of Elros are mortal, following from his choice to be mortal. Would Tolkien have pointed that out, when the other choice would have led to the same result?

Somehow the whole thing seems not clear for me.