Debate and Duel (D&D)

I don't know if it would unbalance the game, but it would make assassins much more survivable. Unless of course they give the Move and Patrol order to armies moving into opponents terrain. Thus nulling the effect of the retreat.

I'm torn on that particular debate because I like assassins, but I don't want them to be a standard fare and make the nations with them suddenly much more powerful while the ones without, would have a significant disadvantage.