There's nothing to suggest that a Personality/Persona couldn't give up it's Duration or that it would make easier for another one to take its' place. Storytelling fiat should always take precedence.
That is assuming the Persona are co-operative. If they have conflicting interests, they could suggest antagonistic personalities or if co-operating, attempt to communicate by leaving messages whiled "Surfaced".
Coming up with objectives is where a lot of drama could be derived from: Rebuilding a relationship or seeking revenge, travelling or staying put, fulfill an ambition or another.
That is assuming the Persona are co-operative. If they have conflicting interests, they could suggest antagonistic personalities or if co-operating, attempt to communicate by leaving messages whiled "Surfaced".
Coming up with objectives is where a lot of drama could be derived from: Rebuilding a relationship or seeking revenge, travelling or staying put, fulfill an ambition or another.