The great end?

[Legolas]

The thought of Arien's fate and the children having Valar were both discarded very early on. Tolkien decided that a great battle would happen upon Melkor's return in the end - the Dagor Dagorath. Mandos prophecied these events - his prophecies can be found in HoME IV and V, along with a ton of other info on "the end." Again, many of the ideas in that were abandoned also, like Turin coming back to slay Melkor. We're not sure that Tolkien still intended the final battle to take place once he reached his last thoughts on what happened to Arda - it became our own world, some three ages later.

A number of threads explain the specifics and discuss the final battle and the end of Arda - just do a subject search with "the end" or "dagor dagorath." Remember, the ideas shifted and Tolkien never really stated exactly what he thought last.

Dagor Dagorath