I think pre-battle negotiations could be a marvelous feature...
Unfortunately it will not work unless CAI/Diplomacy gets a
MAJOR overhaul.
Until then any such negotiations might end up looking like this:
(A Carthaginian full-stack army and a single unit of Town Watch meet on the field.)
Carthaginian General: We will give you a ton of Denarii to disband and leave peaceably; no one has to die here today.
Town Watch unit: Bah! Your bantering of empty words only shows that you are weak and cannot handle the cost of war! Your proposals are rejected utterly!
Carthaginian General:

it bring out the Armored Elephants!