Let me elaborate: a Nord is destined to go to Sovngarde upon their death unless their soul is owned by someone else (such as being a Lycan means you are owned by Hircine) but in the context of Skyrim you are capable of technically giving your soul to multiple sources which is impossible.
Imagine this: a Nord Werewolf becomes a Nightingale but dies in the devoted service of the Dark Brotherhood...who gets this mortal's soul? Nocturnal, Hircine, Sithis, or Sovngarde?
Are there strict contract stipulations that the Aedra and Daedra (and Sithis) abide by? Is this some weird supernatural legal case?
With so many ways to lose ownership of your soul it seems likely that this question would be answered already but I have not yet seen it...