[Saraphim]

I think I actually read something about it in the Silmarillion. But it is very late and I could be thinking of Morgoth's Ring.

But yes, there is a passage somewhere that says that Morgoth and Sauron will return from the Void from which they were cast and do battle with the Valar, Elves, ect.

Try reading the HoME series, or even skim the indexes for Dagor Dagorath.

*this has been useless late-night dribble. thank you for listening.*