you pretty much have to cut the wire just before the bad spot. And restrip. it will shorten the length yes, but nothing much you can do. it probably failed right at or inside the strain relief like they always do.

I cant remember if the wire is fused with the strain relief. If it is, you can cut out the strain relief and then clamp it down and drill out the center. and feed the good portion of the wire through.

If your really up for a challange, i dont know if you can disassemble the DB9, but you could pull all the wires out of the outer sheathing. Then use a small steel cable and fish in new wires. That would be almost impossible, but it COULD be done...