Hi. First, those Molex connections are pretty much standard across the board, meaning, if the periphial has a molex connection, you can pretty much use whichever one is handy. Why it pulled the pin out, when you unplugged it, I don't know. It shouldn't have. Could have been a weak connection to begin with. Anyway, with out that pin, you are right your Data is marooned on the Hdd. One reason why you should back stuff up elsewhere. Anyway, without the pin, you will not be able to use the hdd. You can try to refix it as that seems to be the only option you have. There are companies that specialize in retrieving Data from Hdds, but under this circumstance, I don't know if they can. They are also expensive.
Just solder a yellow wire to an appropriate point on the HDD's PCB, and then splice the other end into a yellow wire in the PSU harness. You could use a male and female spade connector to facilitate easy connection and disconnection.