A Few Thoughts on Ragnarok.

In the Norse prophecy of Ragnarok, the gods and all of humankind expire, the world drowns in fire and ice, and even the sun and moon will have been swallowed by Fenris. However, after the fires cool, the sun's daughter will take her mother's place and, born from Lif (Life) and Leifthrasir (Life-Yearner) two humans who hid away in a cave, new life will repopulate the Earth. (See the “Lay of Vafthrudnir”, and its summary in the “Gylfaginning”).
In Wagner's Gotterdammerung, he places Ragnarok in the context of the saga of Sigurd and the early Germanic people. In the opera, humanity doesn't die, but only the gods and all influence of the gods on earth, including Siegfried (Sigurd), whom he styles as the last of the Volsungs. This is significantly different from the legend, and, in fact, Wagner's vision before he began writing the opera, but it does still in corporate the idea of the rebirth in a modified form. Now, the gods dieing allows for men to live in a world free from their influence. And this allows the men to become gods themselves. In the absence of deities, they are now held self-accountable, man is finally responsible for his fate and there is much rejoicing. Think of this in the context of the world at the time. Nietzsche says God is dead (see, The Gay Science), and he tells us to mourn it (requiem aeternam deo), but Wagner says, delight, for only now can you reach your full potential.
Wagner, uses Ragnarok as a social allegory rather than a religious one. However, other writers are fascinated by it just the way it is. Among these are Tolkien, whose Middle Earth (Midgard) books actually take place on our earth in the distant past, with Ragnarok happening long after the events of his novels, yet still before modern times. Tolkien's overall timeline can be better examined in C. S. Lewis's Space Trilogy, which shows God has this sort of rebirth happen time and again throughout the cosmos. The final book of that series, That Hideous Strength, takes place on Earth and references Numenor, Tolkien's Atlantis. (Incidentally, Lewis mentions that Merlin is that continent's last survivor, leading me to suspect, that, perhaps, Merlin and Gandalf were, at least at one time meant to be one in the same. Though Tolkien's essay on the Istari in Unfinished Tales doesn't mention Numenor in the context of Gandalf, so perhaps he changed his mind, or I am reading to much into it, or else it is simply meant to be vague.) The point being we see that Tolkien interprets Ragnarok not as a prophecy but as something that has already happened, and that we are the descendants of Lif and Leifthrasir (Noah and his wife).