I am playing my first long campaign (1861).
I engaged in a very large battle near Alexandria VA (initiated by CSA) in July 1861. I won the battle, but was unable to find a corps commander (Patterson) after the battle. It was confusing for a bit, but I eventually found his divisions stuffed into the Army HQ .. his unit was MIA and he was no longer in the roster list. The rules semed to indicate that 3-star generals at corps and army levels are nearly impossible to kill in battle .. what gives here? Also, if a general is lost during a battle, where are you informed of this? I believe an event of this importance should be included in the event list for the turn and on the battle results screen.
There is an event which fires between the end of July '61 and the first of September '61 that automatically removes Patterson, presumably due to incompetence (Patterson not retained). This event probably occurred and you overlooked the event message. There is an ongoing debate to remove some of these (automatic removal) events. However, think of the alternative: An incompetent Patterson or Fremont remaining in the game and interferring seniority wise with the promotion system all thru the war, regarding Grant, Sherman, etc. and the National Morale points system Union hits that would continually occur.