The Elves all leaving for Valinor was a mistype. I was thinking and speaking more of the realm that many of them HAVE left and are leaving.

[quote]Melkor's lies, sowed in the hearts of Elves and Men, were a seed that did not die and could not be destroyed, but ever and anon sprouted anew, and bore dark fruit ever after.[13]
According to material in some of Tolkien's writings compiled (but not published) by his son, in the last days Melkor will learn how to break the Door of Night and re-enter the World, and initiate the Dagor Dagorath, the Battle of Battles.[14][15][/quote]

Morgoth is darkness, lies, deceit. And while you may win a battle or war against him. He will continue. As he is immortal, As he was once joined with the Valar, Blessed by the hand of Eru. He can very well return.