Looking at the socket 1155 pinout, it looks like a ground pin near the voltage supply. There are tons of ground and voltage pins around it, so
IF that pin is the only thing that's wrong with the socket, you'll be fine. Make sure that it's not bent and touching another pin, though, or you could get a short between power and ground.
However, without understanding the history of the board (why/how is that pin disconnected?), it's impossible to say if you'll be able to boot or not. It seems like a strange failure, and makes me wonder about the condition of the other pins and the board itself.
Edit: For reference, here's the link for the socket 1155 pinout:
http://www.abload.de/image.php?img=pins_sandyamb4.png. It's from Sandy Bridge, but since SNB and IVB are socket-compatible, it doesn't make a difference. Rotate it 90 degrees clockwise to make it line up with your picture.