Dior

[Mhoram]

Thingol, you need to be more careful with your quotes. It looks like all that is in the quote box if from tolkien's letters, when actually only the first sentence:

In the primary story of Lúthien and Beren, Luthien is allowed as an absolute exception to divest herself of 'immortality' and become 'mortal'

is actually from Tolkien.

We don't really know whether Dior was full mortal or half-elven with a choice, because he was only 35 to 37 when he was slain.

There are two possibilities.
A) He was half-elven with a choice.
B) He was full mortal without a choice.

We know that he wedded a full elf and their children were half-elven with a choice, we know this because their daughter Elwing made a choice.

This holds true for both A and B. Elrond was a half-elven who married a full elf and his children were still considered half-elven and given a choice. And if he had been full mortal, having married a full elf, Elwing and brothers would still have been half-elven.

I would personally assume that Dior was Half-Elven and decided, or would have decided to be counted among elves. I feel this way because he was accepted so happily as king of Doriath.

Of course, much of what we know comes from Christopher Tolkien instead of John, because the Ruin of Doriath had to be written mostly by Chris. *shrugs*