Board Thread:Lore Discussion/@comment-72.77.73.35-20140408131341/@comment-82.23.138.127-20150210214652

As others have stated, the pact made with Nocturnal was a concious choice made by the Dragonborn. There was no accident, no foul play. The Dragonborn willingly forfeits his/her soul to Nocturnal. From that alone, Nocturnal would have more rights to claim the soul than Hircine or any other Daedric lord seeking the soul of their champion. Additionally, the prerequisites are never really confirmed for joining Hircine's realm.

All we know is that if you're a werewolf alone and die as one, you become part of Hircine's realm. It isn't ever suggested what occurs if the soul is already forfeit and promised to another Daedric lord. Whichever Daedric lord a pact was made with first, logically, we would believe that they have the right to claim first. Although, these are Daedric lords, so perhaps your protagonist would choose between them or the Daedric lords would send champions to duel for it. It is a good question, though lore wise, it is unknown.