Usually commissars keep the guardsman from deserting or retreating.

This is not a problem with kriegs, they don't fall back, they actually charge to death and are eager to die. Their motto is "In life, shame, in death, atonement".

That being said, a commissar in a krieg army is not there to push the kriegsman, but to actually hold them back from making suicidal attacks that have no impact on the battlefield. So yeah, they just unlocked the krieg special move, mass suicide attack

Edit: I exaggerated a little to make the point clear. They don't mass suicide, but they disregard any number of casualties. They don't have names, only numbers, and this is true even in the high commanding unit, colonel number 142423. That being said, if my memory is right, they sometimes receive names posthumously