AI loses aggro when you’re outside view for a few turns, you can plan some movement running into the bushes, but it depends on your speed as well. If you’re slower or same speed it might be difficult to run away and not aggro someone else.
Rasimi has +10% speed over regular humans so it can be easier to run away, while Lizardman is very fast when running on the water tiles, so running across the river can get you out of sight fast.
Nomads have the ability that increases movement speed for a short duration that helps too. Berserkers and Knights get charge and lunge that can help as well. Poachers get rollback.
For slow characters without any move abilities, not getting aggroed where you’re not ready to fight to the death is probably the prefered tactic though.