What happens next?

The simpler the solution...

"What just happened?" asked Joyce-in-Tara. "Why am I suddenly outside of Faith's body? Am I having what people call an out-of-body experience?"

"No, you aren't, Mrs. Summers," said Tara-in-Faith. "You just accidentally activated the body swap talisman. Now I'm in the body you were just in and you're in mine. However, if we just squeeze the talisman again..."

"Oh, no, you don't," said Faith-in-Joyce, rising up from the floor where she had been lying. "You're not switching anything unless I get back in my old body first."

"How long have you been conscious?" asked Tara-in-Faith.

"Just long enough to see you two make fools of yourself with this body swap deal," said Faith-in-Joyce. "Now give me that thing."

"No," said Tara-in-Faith, holding the Draconian Katra away from Faith-in-Joyce.

"Yes," said Faith-in-Joyce.

And before Tara-in-Faith could say anything more, Faith-in-Joyce was upon her.