WMG / Sweet Home

Eun-hyeok turned into a monster in the last episode

We don't actually see him die onscreen, nor do we see his body. The last we do see of him, the camera focuses on the photo he's holding as blood drips on it. We already know Eun-hyeok is infected, and the blood looks very like the nosebleeds that warn an infected person is close to becoming a monster. Hyun-su demonstrates infected people can survive falling at least six storeys and being shot repeatedly, and fully-transformed monsters can only be killed with fire, so it's possible Eun-hyeok survived the building collapsing on top of him. For that matter, the other monsters still in the building probably survived it too.