Reading this chapter in WN form was thrilling, but GOD DAMN do they do the kinetics of the visuals justice with the artwork, here! Got chills, goddamn!
First, his teleport has a few hours cooldown, that's why he uses the dragon instead. About the ogres, the chief/captain/leader of the ogres is stronger than the ogre shadows, so they'll keep getting destroyed and regenerating until MC arrives.
Outcome :
Sister is fine, MC will arrive at the last second, and pissed off. Ogres get destroyed while Igris evactuates with the remaining students. Sister wanted to stay with her brother, in tears, before being evacuated.