I don’t think we need a forget target option, the move command should work for that. At the moment, I’m pretty sure all combat units are always aggressive which would explain the behaviors you’re seeing. There’s a note in the code about passive stance being bugged - I’m guessing it has to do with combat units wandering off in previous builds. So their temporary measure was make everyone in a party aggresive; not ideal, but hey it’s better than wandering guys.
Our soldiers are here to defend their town. I don’t want them running away because they’re sore and have villagers die. They stand and fight and die or I’ll leave them on an island to starve. 
When the passive option is fixed, you’ll be able to command move your unit away from the fight and they won’t engage beyond 60-some blocks of their field of vision. Right now though, even if you try to move them there’s a good chance they’ll turn around as the move action isn’t passive, it’s aggressive.
If your combat unit is in a party, and the attack standard is still on the ground, even if you move a dying unit far away they’ll return to that flag as it’s the party component driving that behavior.
Basically, everything you guys want the game can do. One piece is broken and frustrating - passive/aggressive, the other needs intervention on your part - party/move and/or remove dying unit from party and hide in town.
@sdee or @linda Are my assumptions correct? I think we could use a reminder on how party mechanics and the attack/move/defend banners function 
If I’m out to lunch, feel free to call me on it! .