Cheong San, one of the key characters in the series, was actually a bit of a supporting character in the Webtoon. In the series, Cheong San was able to survive as one of the main characters, not until Gwi Nam fought against him—hence, leaving both of them inside a building that eventually caught the explosion intended for Hyo San’s groundzero.
In the Webtoon, Cheong San had a different ending. He was actually presumed to have been eaten by zombies during the rope scene. In the drama, this is similar to when Cheong San thought of using a DIY rope so they can escape through the window and then safely settle in another room—here, they decided to stay in the recording room. But, in the Webtoon, they went up the rooftop to call for help—the SOS equivalent scene in the drama.
However, in the Webtoon, Cheong San wasn’t able to join them at the rooftop as he was already bitten by a zombie. Instead, he decided to stay in the classroom. He also gave his name tag to On Jo during this scene, and then assured her that he will go to where they are if he ends up being immune like Nam Ra.
Minutes passed, and he never went up. That was the last time the group saw him.
The Webtoon never showed Cheong San’s body. Although it was implied that he didn’t survive, not showing his body in a graphic comic may signal a possible return. There’s a possibility of him being alive by creating that opening. Not to mention, Cheong San is an important character in On Jo’s life.
In the drama, we also don’t know if Cheong San became a half-bie / hambie, and if half-bies can survive an explosion. Although there was a scene showing the bodies in the building where Cheong San and Gwi Nam fought, On Jo never saw his body. This creates another opening, if the production team decides to turn him into a half-bie.
So, yes, it is presumed that he didn’t survive. But his character has an open ending that can be tweaked if needed.