Most of the Top of the Rock has tall plexiglass walls, as you can see at the bottom of the photo. Those parts that don't have the other level just below them. Pushing someone off that ledge might give them some bumps and bruises a broken bone or two depending on how they land, that's all.
Nice photo... Some guy is sitting on the edge of building and takes photos.... and suddenly BOOOO!!! -Oh, wait I didn't wanted to scary you, where have you gone?... Uh, what is this strange red thing down there on the street... and police sirens? XD