[Ibrîniðilpathânezel]

If I'm recalling his intro to the book correctly, Foster out-and-out refuses to include any information that doesn't appear in TH, LotR, or TS. A good example is his comment that Gandalf "may have been a Maia," and that it is "tempting" to equate him with the Maia Olorin. Tolkien plainly says in Unfinished Tales and in many other writings that the Maia Olorin IS the wizard Gandalf, but it didn't show up in the "story books" (for lack of a better term), so Foster disregards it. For me, that doesn't make him the best source for definitive information about Tolkien's works.

Anyway, I think there is one other factor to be considered in the fates of Elladan and Elrohir: their mother. They chose to go to war in Gondor with the Dunedain not because they strongly identified with mortal Men, but because they "remembered the torments of their mother" at the hands of the Enemy when she and her party had been attacked while traveling from Lothlorien to Rivendell. That they would be so strongly driven by this event, which happened many years before, is, to me, significant. They may have stayed for time after Elrond departed, perhaps because of their sister, but also perhaps because they wanted to be sure the remaining Enemy forces were defeated and either eliminated or no longer a major threat. In the end, they may not have been around when Arwen died because they desired to see their mother, healed and alive again. It was because of her that they fought so strongly against the Enemy, and I find it hard to believe that they would not want to see her again. Just a thought.