I suggested a while ago, in regards to the "no loss" craze that has taken ahold of most us at one point or another...just incorporate a main quest that involves sacrificing a unit(s). That way 0 losses would not be obtainable.
Of course, people will then do the "Excluding the
Sacrificial Quest I did a zero loss on impossible" rant.
How about impress me...ONLY have 1 peasant, and finish with no losses on impossible! That would be impressive!