What happened to Mordor?

[Sir Kohran]

They had come to the desolation that lay before Mordor: the lasting
monument to the dark labour of its slaves that should endure when all their
purposes were made void; a land defiled, diseased beyond all healing --
unless the Great Sea should enter in and wash it with oblivion.

What a great piece of writing.

That would mean the Bibical Flood that Tolkien predicted at the end of the Fourth Age.

Very interesting - in The New Shadow, Tolkien planned to have Gondor fall into decay and evil practices once Aragorn had died. Perhaps that story would have ended with God becoming angry with all the evil Middle-Earth had fallen into and flooding the world, only saving Noah and his family - this would remove the last traces of Middle-Earth's history from the world and lead into the rest of the Bible and then towards modern history. Did Tolkien plan something like this?