Crimson Honor Guard's last ability triggers at the beginning of each player's end step whether that player controls a commander or not. Whether that player controls a commander is checked only as the ability resolves.

The player could control any player's commander to satisfy Crimson Honor Guard's ability. If a player gains control of another player's commander “until end of turn,” the player who gained control of it will still control that commander during the end step.

Crimson Honor Guard will deal 4 damage to you, too, if you don't control a commander.