Once a schedule has been published, you can not set the schedule to go back to unpublished (draft),
as Tasks have been planned and the assigned Resources have been notified via email
but you can continue to make changes by editing the existing schedule via the Gantt.
Published schedules can only be deleted if they have no tasks assigned to resources
OR marked as closed which means the schedule will continue to be visible
but any incomplete tasks will be marked as cancelled.