We all know that Lorkhan/Aka and Jygg/Sheo are enantiomorphs and mirror each other. Buut...

Lorkhan is cursed by the Aedra and his heart is removed. Jygg is cursed by the Daedra and he goes mad (supposedly when Lorkhan's heart is removed). The Shivering Isles are then subject to Sheo turning into Jygg and then destroying it at the end of every era. The Mundus is also subject to Alduin destroying it at the end of every kalpa. So the question is, does Lorkhan turn into Alduin as Sheo turns into Jygg? Remember that the Greedy Man turns into Thartaag the World Devourer. Is that why Shor was gone from his halls and as Jygg was sent to the waters of Oblivion, Alduin was released into the skies of Aetherius?

Just a thought.. not sure if obvious or stupid.

I think Jygg's release had nothing to do with Alduin's return. They both just happened.