A escolha da mortalidade é permanente.
Depois de escolher o Dom dos Homens, você é mortal e todos os seus descendentes serão mortais. Somente se você permanecer imortal, seus descendentes terão a escolha de serem mortais ou imortais.
Nas palavras do próprio homem:
"The view is that the Half-elven have a power of (irrevocable) choice, which may be delayed but not permanently, which kin's fate they will share. 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: so Aragorn (who, however, has a greater life-span than his contemporaries, double, though not the original Númenórean treble, that of Men). Elrond chose to be among the Elves. His children - with a renewed Elvish strain, since their mother was Celebrían dtr. of Galadriel - have to make their choices."
-- Tolkien, Letter No. 153