[Mithalwen]

I don't see why Dior would get a choice. He was born to two mortals ans so woud have been mortal. Like the offspring of Elros. He married an elf of course and their children were therefore halfelven, unless an unrecorded exception was made he would have shared the doom of men. However I would class Elrond as an elf comparable to the children of a Japanese friend who have an English father. Half and half by ethnicity but fully British by nationality, though they had the option of taking Japanese nationality up to age 18.