I don't think Hisoo died because there seemed to be another person also on the ground.

i don't think anyone dies. i think it's one of those dramas where they try to make it look like someone died(yet they survive/recover from the injury later).  however that may be the beginning of just another twist in the story.

I didn't expect that Ha Ji Yong would died from the stairs because at first I was expecting Ja Kyung or Hui Soo