Well, i would call that cheesing the AI. If the AI loses its target it goes back to the state it was before the attack, looping from there. While that may seem broken or illogical i think its not. It would be nice if the AI would go into an "alerted" state for a while after the first attack to not get surprised anymore and be able to
attack the next time. Depending on the enemy. Stupid mobs should just stand around dumbfouded. I like that.
That selfheal after such an attack is something that annoys me to no end...while for enemies capable of healing it is totally ok, mobs that are not should be able to be cheesed. Hit n Run tactics may be not the fairest of things but are totally OK.
If a developer wants a certain encounter to be not cheesable a certain way they should get their heads spinning to create a battlefield tactic for the AI that makes this impossible. Just having the Mob re-heal to full is just fking lazy.