User blog comment:Pelinal Whitestrake/About Aka, Lorkhan and broken Windows/@comment-24758713-20141117162447

It's just a theory Alduin was absorbed by Akatosh. Alduin could have been absorbed by Sithis/Lorhan to re-build his own strength (after all, it's his realm where Alduin died), or he could have returned to Aka-Tusl/Aka (I believe Aka-Tusk is the original shard. Aka, I believe, simply doesn't exist.) Or maybe, he didn't die at all and simply...a dragon-break happened. Both Alduin and Akatosh are dragons. Something weird happened, because we are the only dragon (As we are the Last Dragonborn) in Shor's realm. Shor wouldn't allow Miraak to absorb Alduin's soul. So, we can only spectulate.

(Note that Lorkhan was evil, as his intentions were bad. Nords' Shor was benevolent, and hence he is a good type of deity. Kind of like God Himself, if you ask me)