1) in editor, set player as leader of group of playable infantry units (like in a mission designed for COOP)
2) start mission
3) when player (as group leader) is killed, and
4) player team switches to a squad mate, and then
5) player chooses "switch to group leader" from Action menu, and group leader is dead,
6) game must be killed, as neither ESC or any other key can be used to quit or revert mission.