The glyph appears to have multiple runes about it. You aren't sure what the multiple combinations of runes do. Some might turn off the gas, while others might open the doors, but opening the doors without first turning off the gas would be a problem. It is also possible the glyph is rigged to explode if you give an invalid command, though that is only an assumption.
Chironides peaks around the hallway and sees an elaborate room with intricate double doors on the north wall. This definitely screams "I lead to a throne room". The hallways does continue, though, and looks to lead into a natural cave.
As for Isaiah, he is trapped on the southern side, any closer north than the end of the bridge will result in inhaling poisonous gas. The gas isn't opaque and has no odor, but you can sense its presence as you near the end of the bridge. The only opening you see so far is a wooden bridge to the left that leads somewhere no one has gone yet and that is about 35 feet away and 15 feet lower than the bridge you are on.