Board Thread:Lore Discussion/@comment-27038858-20151003072000/@comment-26998063-20160127180156

High King Emeric wrote: Silver4Raven wrote: "You can break my body, but you can't break my soul," is basically what it means to be dragonkind... Unless you're a dragonborn, you cannot kill the dragon's soul, which means you cannot kill the dragon. Does that make sense? It should. Alduin is not dead. He's very much alive, somewhere on Nirn. If he hasn't been resuscitated, he will be by the next era to battle the next Dragonborn, who he may defeat and destroy Nirn. Wait1 You said that a dragonborn can kill a dragon. But Dovahkiin can't? Dovahkiin and Last Dragonborn or any Dragonborn are the same person. Dovahkiin is a name given to a character by the dragons that translates to Dragonborn.

Alduin was not sent back in time before. he was sent forward in time. My guess is that he was not sent back or forward in time and his soul is simply at rest for the moment and likely will rise again sometime in the future of the TES timeline.