Responses
Hellfire is his most powerful spell, and the enemy girl herself was surprised about how powerful a more simpler spell was, it isn't surprising that hellfire would put her in bed.
He retreated because he only had enough mana cast one hellfire, and that dimension/necklace was impeding him of recovering his mana.
They we're about to retreat but they also have to report the events first. Is that what's confusing you or something else???
Missing pages? How did it go from "we should retreat" to "the princess almost got killed"?