If one character dies while wearing a ring that already has a soul, the official ruling is that only one soul can be in the ring at any given time. Of course, a savvy DM can play with this. The characters can switch places with one another when the attuned owner dies, the soul inside the ring can be banished to their afterlife, or perhaps the wearer’s soul doesn’t go into the full ring. You can do just about anything if you want to have some fun with it, and it could even be determined by the person inside of the ring. An evil wizard might want to take over the character’s body, while a fallen adventurer might seek closure for his death before willingly departing for the afterlife. Think about it when you give the player the ring because this item is ripe with storytelling potential.