If she's really dead and they don't have a way to resurrect her, I'm going to be very pissed. She's a lot more interesting of a character than her little sister.
I assume she's gotta be alive, because if she was really dead he'd probably just have carried her head since it'd be lighter + a more effective immediate threat.
I'm manga only and haven't read ahead, but I'm gonna go out of a limb here and say she becomes a monster he can tame... I'd be surprised if the author had an original neuron in his brain and it wasn't that.
so....she fought the guy and they ran off, and hes right behind them maybe 10 seconds later. He knows where they are in the castle after floor changes, with a huge battle going around. Silly pacing.