Would the Half-Elven vanish if they wore an elven ring?

[cellurdur]

Originally Posted by Puddleglum

I wonder if this is only a semantic difference (my apologies if I am misunderstanding your meaning, it's not intentional). Silmarillion seems clear that she become mortal "Then she would become mortal, and subject to a second death". Whether than means she became specifically Edain (or did you mean to say Atani?) or not seems less important to the question of whether her fate as being part of the larger classification of "mortal" (having the gift of Illuvatar vis-a-vis departing Ea forever) had implications for her child, Dior.

Luthien remained an Elf. Humans cannot use the kind of magic Luthien throws around. She alone became a mortal elf. Luthien would not suddenly start getting sick, be unable to walk on snow, lose her eyesight etc because she was mortal. The only change was inwhat her fea would do after death.

The general rule that seemed to be followed was that, if both parents were Mortal (had the gift to depart), then their children would have that gift as well. If one or both parents did NOT have that gift, the matter was uncertain (at least until Manwe made his ruling).

No there was no general rule. It had not been decided what to do with the Half-elven until Manwe made his ruling. Then it was decided that ALL people with a drop of mortal blood would be mortal, unless an exception was made.

Elwing's brothers are, indeed (I think) a case we are never told about. Maybe, since they came to Valinor via death (ie, straight to Mandos), Mandos treated them as having the gift and they departed without the matter coming to Manwe.

In Elwing's case, she had broken the Ban of the Valar by coming, in the flesh, to the Blessed realm (with Earendil). That sort of forced the issue and Manwe had to make a decision both formal and public.

Mandos is not going to let such an important decision go without discussing it with Manwe. In the case of Earendil he was in a bad place, because as Noldor or as a man of the HOuse of Hador he had broke the ban either way. So Earendil coming to Valinor did not really force their hand to decide, because they both punished and rewarded him either way.