If the players are on a course and they choose to leave the world (via other plugins etc.), their ParkourSession should be destroyed, without trying to teleport them away.
This should be configurable, as there is currently a setting to prevent players from teleporting away from a course.

This might be a similar work to #191 with the need for silent leaving of courses.

In Parkour v6.0 a new setting "OnCourse.EnforceWorld.LeaveCourse" will silently kick the player from the course when teleporting to another world.