The answer is no. In combat, you cannot retreat. You either have to win or lose the fight to make it out of combat. you may only retreat from enemies if they chase after you on the field, as you can move away from them, and the aggro will eventually die.
Or by hitting retreat on the battle interface before the battle happens. Sometimes, the retreat option is greyed out if the fight is story-based or a tough battle, so you cannot retreat. You have to fight.
Related:How to complete the Three temples Under God side quest in Disciples: Liberation – The Plain of Widow
These are the only two methods to retreat in the game. You can reload your save by quitting the game and reloading the last autosave. The autosave usually is pretty generous and will place you before the encounter. But this is generally towards more important fights than random encounters. So do this at your own peril.
If you are unsure about an area or a fight, feel free to save constantly or abuse the quick save system. This will keep creating save files for you to load.
