In rare cases, a sent spirit can leave the Farplane if they still have an attachment to the world of the living strong enough to prevent them from moving on to the next world. The only occurrence of this known to the player is when Jyscal Guado briefly leaves the Farplane to give Yuna a sphere ofSeymour.
A spirit doesn't necessarily need to be sent in order to find its way to the Farplane; in fact, as there are only a limited amount of summoners, and their main job isn't performing the sending, but, rather, completing thepilgrimage, it is likely most people do not need a sending. Sending is required most commonly when a person dies in violent or otherwise unusual circumstances, as their spirit still has "unfinished business" back in the world of the living. Once an individual has accepted death, they will return to the Farplane without the need of sending. Even the individuals who go on to become unsent are shown to possess this ability. )