
Both game end modes and all of the existing ones (and many more) could be represented by a field and a checkbox:
Checkbox title: No commander, no control
Explanation: If this box is checked, a player with no commanders cannot control their units.
Field title: Number of commanders required
Range: 0-16
Explanation: The number of commanders required for a team to stay alive. 0 means that all a team's units must be killed for them to die. 1 means that all a team's commanders must be killed. If the value of this field is equal to the number of players on a team, then any commander's death will kill the player's entire team. If the field is negative, then it will be interpreted as (number of players on team) + (field).