The published Silmarillion ends with the recounting of the voyage of Eärendil the Mariner, but in the older versions of the Silmarillion as published in The History of Middle-earth this was not yet the end. The Silmarillion originally ended with a prophesy by Mandos about the Final Battle (or the Dagor Dagorath in Sindarin).
According to the prophesy, Melkor will discover how to break the Door of Night, and will destroy the Sun and the Moon. For the love of these, Eärendil will return from the sky and shall meet Tulkas, Manwë (or Eönwë his herald) and Túrin Turambar on the plains of Valinor. All the Free Peoples of Middle-earth will participate in this final battle, Elves, Men and Dwarves alike. To their number will be added Ar-Pharazôn and the Númenóreans who landed at Aman in 3319 SA.
There they shall fight with Melkor. Tulkas will wrestle with him, but it will be by the hand of Túrin that finally death and destruction will be dealt to Melkor. Túrin will run his black sword Gurthang (Iron of Death) through Melkor's heart, thus avenging the Children of Húrin (Sind: Hîn Húrin), and the Pelori Mountains will be levelled. The Silmarils will be recovered from the Earth, and Fëanor's spirit shall be released from the halls of Mandos to unlock them and rekindle the light of the Two Trees. The battle will happen at the end of Arda's existence, and mark the ending of the world, finally ending the immortal life of the Elves.