Are we all in accord that the missing piece of the prophecy spells the sealing of Castle Town? Not to mention that it's named after the player, so it's very likely what Angel's Heaven is supposed to be.
This would also fall in line with both Susie and Ralsei's reactions; one knows that he's gonna stop existing soon and thus considers himself a means to an end, trying to depersonalize himself as a coping mechanism, while the other does not want to lose her dear friends and will try to find another way no matter how much she'd have to bleed for it.