randomize scenario?

[gila]

What you are asking, is not too hard to create in a single battle.
Say a Dunkirk situaton where you would have to evac as many as possible,then have results on how many survived.
Another could be a fighting withdrawal in Arnhem.
Endless other possibles

[Imp]

For search & rescue type missions the % chance of reinforcing works quite well the other slightly longer approach which should work is to do a branching campaign. Say 4 similar scenarious, save the first shift some guards etc & save, repeat then make a branching campaign with equal chance of selecting any of them so you dont know which your playing. wait 6 months & take it for a spin.