[Elladan and Elrohir]

Well, we simply don't know the answer. The only unknowns, when it's all said and done, are Elladan and Elrohir. Tolkien says in his Letters, and Legolas (the Downer, not the Elf) alluded to it, that just because they didn't go with Elrond, didn't mean they were choosing mortality. They merely delayed their choice.

I would guess that if they remained in M-E past a certain point, that they would indeed become mortal. But what would that point be? Perhaps after the last ship had departed the Havens? But that's mere speculation.