Board Thread:Lore Discussion/@comment-26177830-20150401044533/@comment-121511-20150405000833

Alduin is not the only indestructible being in the Aurbis, and that is implying he indestructible in the first place: the only beings who are truly permanent, incapable of erasure, are those who have achieved CHIM. That said, he cannot destroy Souls, he can only siphon power by "consuming them": nothing can destroy Souls. Alduin is far from an omnipotent God, and indeed is defeated in Skyrim by a mortal Hero. No God in the Aurbis is omnipotent, as they all have limits to the extent to which they can apply their power.