When the world is much older and the gods weary, Morgoth will come back through the door and the last battle will be fought. Fionwe will fight Morgoth on the plains of Valinor, and the spirit of Turin shall be beside him; it shall be Turin with his black sword who will slay Morgoth, and the children of Hurin will be avenged.
In those days the silmarils of the sea, earth and air shall be recovered and Maidros shall break them and Palurien with their fire rekindle the Two Trees, and the great light shall come forth again, and the mountains of Valinor shall be leveled so that it goes out over the world, and gods and elves shall grow young again, and all their dead awake.
That is one of the versions of Armageddeon in Tolkien, another version differs only in the fact that Melkor destroyed the sun and the moon and Earendil shall come down and drive him from the sky. Once down instead of just Fionwe and Turin, Tulkas will strive with him, Fionwe on his right and Turin on his left.
Another version is completely different. For 'tis said that ere the end Melko shall in somewise contrive a quarrel between moon and sun, and Ilinsor shall seek to follow Urwendi through the gates, and when they are gone the gates of both east and west shall be destroyed, and Urwendi and Ilinsor shall be lost.
So shall it be that Fionwë Urion, the son of Manwe, of love for Urwendi, shall in the end be Melkor's bane, and shall destroy the world to destroy his foe, and so shall all things then be rolled away. Turambar indeed shall stand beside Fionwe in the Great Wrack, and Melko and his drakes shall curse the sword of the Mormakil.
I find it interesting to note that in the first two versions of the end, only evil is destroyed and then fate is doled out where a joint effort (Fionwe, Turin; Fionwe, Turin, Tulkas) is made to destroy Melko, whereas in the last version Fionwe destroys the world and his foe with it. Turin does enter in but has no part in the slaying of Melkor; he does do great deeds however.
(I'm proud of you son, ya killed the greatest evil in the world! :)----Hurin-V)
In a last and final version there is a battle of the upland heath under the sapphire raiment of Manwe. It is said if Humans side with the Valar then the elves shall yet survive for awhile upon the earth, but if they side with Melkor in that last terrible battle, then the fading of the elves shall be complete and never shall their like be seen again upon the earth. Thus the End of all Things, Armageddeon, Ragnorak, and of course Dagor Dagorlad.