Why are you so worried about this? The hentai scene depends on Amber's choices. If she fights, another character comes to Amber's aid after she loses.
I tried playing for a while after the fight and realized one of my worries was unfounded. Even so, I don't like losing fights. Personally, if an enemy is going to defeat my character no matter what, I'd rather not have to play through the fight and have the defeat happen via a cutscene or with dialogue.