I don't think Robert E Lee was a great general, just a great and humble man. Stonewall Jackson and "old blue eyes" Longstreet were the tacticians, along with their commanding lutienants, Ewell and Hood for example. The only thing that took the Union forever to win was their complete lack of unity and drive. Gettysburg was a victory for the north but tactically it was still a loss for the Army of the Potomac as they let Lee south again. The king of spades was a defensive minded general in a world that was becoming a defensive fighting force and World War 1 proved that trend out to its peak.
It's not really a bad rule when you think about the Feudal chain of command. When the man in charge dies then no one could possibly replace him because back then he was usually "graced by god" and all that. All of his banner men pledged their lives and now that he is dead, the pledge is upheld and the job is done.
"Get the heck out of here before we die too!!!"
The only time I lose my general is because the game is over on my opponents next turn unless I can somehow squeak out this last win so I put my general in the fight just to add the 2 attacks to help the odds.
I find that the usual breakpoint rule works really well for campaigns, you win a fight and push your enemy back but you didn't kill any of his good troops so the next fight will not be as easy as you might think or heck, your enemy might attack you back immediately. Also, the breakpoint rule really makes a player cycle his troops and try to use them all which is a strategy that feeds well off of the ordering system that Rick Priestly set up for the game.....I think anyways. I always beat my brother because he refuses to cycle his troops and usually just pushes his cavalry forward until they are all dead and then I come to kill his infantry

Cycling troops was also a good strategy back in the American Civil War, just to bring it all back around.
My wish on the subject is, I wish it was easier to kill the characters, at least just the heroes and spell casters and to break down the command structure that way, making my opponent really use the command structure this game is based on.