You think THAT is confusing? You want to know what is truly strange? Sans and Papyrus can both die, but we never see or hear their souls breaking in the canon game. They are either actually immortal, or they never had souls to begin with, neither of which makes sense. If they were immortal, then they can't die, but they can, so they aren't immortal. And if they were already soulless, they wouldn't even be alive in the first place.