Cable Plug-in Portion Destroyed

Although this guide doesn't show opening the cable side of the headset, the practice is the same.

Inside the cable portion of the head set the cable should be connected with some solder, simply heat the solder with a soldering iron and the old cable should come right off, and simply replace with a new one.

Or

you have just clip the cable above the damaged area and splice the cable with a new one, and cover with some heat shrink tubing or electrical tape, which means you don't have to open the headphone, but it's a bit ghetto.