Imagining that the Silmarillion and other such texts (Unfinished Tales, Lays of Beleriand, Lost Road) are received texts (those that come down to us by means of our heritage), the North would necessarily have been literate long before it was in actual history. It would still have been saddled with the "flat earth" world view, which would put it on a par with the Greek, Babylonian, etc. myths. The one thing it would be lacking (as Tolkien intended) would be the bloodthirstiness of its greatest heroes and its gods.
Imagine how these things might have affected Germanic and Celtic history, say, around the time of Alexander the Great? or Julius Caesar? or Marcus Aurelius? Constantine? Charlemagne? The implications are vast.
(By the way, it's "what if" questions like this that get us fiction writers really going!
