As previously stated, in most cases (i.e not when the Führer was in a grumpy mood) generals were evacuated for several reasons. And as for generals running the risk of dying during regular combat, I'd rather not see it implemented. The frustration of loosing for example Heinrici during a two hour battle against suicidal beach attackers on the Atlantic Wall would not brighten my spirits very much at all. Plus, I think most commanders had the sense to stay away from the dangers of combat, they knew their own importance, and weren't very eager to die in the first place. However, I can agree that there should be a small chance in the case of an encirclment, just for the hell of it. Could be fun and mood-setting. Anyway, if you saw a
Kesselschlacht coming, you could represent the evacuation by switching your experienced, high-level field-marshal for a lowly major general if you knew you were going to loose anyway. See, simple, huh?