system
Given the following post, respond as if you're commenting on Reddit:
human
[LoTR and Middle Earth] Elves that chose not to leave for Valinor and stayed in Middle Earth, what would of happened to them and the areas they lived on

What I mean is, lets say everyone in this sub reddit were Noldor Elves and resided in Rivendell. If we chose to stay in Rivendell for the entirety of the Third Age into the Fourth and so on, what would of happened to our bodies and ultimately Rivendell.
gpt
Ultimately, our spirits (fëar) would consume our bodies (hröar), and we would be left as houseless spirits, a kind of wraith.

When Men die, their fëar depart the circles of Arda for whatever lies beyond - the Gift of Iluvatar. The fëar of Elves, on the other hand, are bound to Arda until its ending. If slain, the fëa of an Elf can go to the Halls of Mandos in Valinor, and ultimately be reincarnated into a new hröa.

This weakening of the hröa is due to the marring of Arda by Morgoth, and the cause of a great deal of grief to the Elves. The Rings of Power were made to prevent this; when their power was lost with the destruction of the One, this process can only be avoided in Valinor. This is why Galadriel told Frodo that, no matter what happened, the time of the Elves in Middle-Earth was over. If Sauron was overthrown, it meant that the power of the Three would be undone, and in time the bodies of all the Elves in Middle-Earth would be consumed by their own spirits.