I've found something. A machine used by the Ancients. I tested it on what's left of Sarah. Apparently she had a bit of her soul left, but the machine drained her dry. As I unstrapped her, she was smiling. Humming. She looked happy.
If souls can be taken, then they can be given. They can be transferred, stored, and restored.
I will figure out how to restore my soul, even if I have to sacrifice every person in Reekwater to do it. I need it more than they do. They have the Song; I have nothing.