more realistic if the person in control of the entire army falls during a battle,
From my very limited knowledge on the subject, I don't believe this was how battles were fought in the Medieval ages. Marshals in feudal times certainly didn't command the entire army as far as I'm aware, this is a unique BM feature.
I could be wrong, but I believe that the individual Lords, and Barons etc. had their own Knights, who served under them. In return for land they were employed to fight for their Lord. If they had wealth, these would in turn recruit their own men, such as men-at-arms etc.
During a battle, you'd be in command of your own men, no-one else would command you or your men, other than perhaps Royalty. (Although in England at least, the Barons were also extremely powerful, almost equaling the Kings power). So I doubt that they or their Knights would have been following a single leader in the modern sense anyway.
I understand that there is one person who can control the unit settings of the entire army in BM (although individual leaders can also set their own unit settings which is a bit more realistic). But I don't think this is how it was in actual Medieval times.
