Back when I used to lead large group hikes, we had a leader in front and a sweep in back. Both had usually prehiked the trail in advance, within a few weeks of the hike. Persons leaving the trail for 'personal business" or any other reason, were asked to leave a pack or jacket or something very visible on the side of the trail. The sweep was to wait at the marker until the person reappeared. The sweep passed no one of the group on the trail.
Group members ALL got copies of the hike directions and a map, along with a list of things to do if "What If" happened. Often, the leader would leave small cards with arrows showing the direction to take at junctions, to be collected by the sweep.