When the existing commander leaves (and their auto-reconnect option times out), I propose that the first person on helm gets auto-promoted to commander (and the commander slot would be once again filled when viewed from the lobby). I've had a few annoying cases where players jump into the commander slot, and steal the helm -- most recently it was a powdermonkey, who clearly had not picked up any skill yet, stole the helm in the middle of a tied-score fight against a then-disadvantaged enemy, and logged out as soon as our team lost the battle.