Originally Posted by
SoldSpartan
What if I just twist the cable together? That is about the limit to my mechanical capability.
Sometimes it's easy to get it to twist up together again. That looks a little worse so I wouldn't expect total success. Some strands might even break. But as long as you never need to loosen the holdfast to adjust the cable, you should okay doing anything you want to do to it. Even doing nothing is okay.
Bunch it together if nothing else and put some heat shrinkable tube on it. Or just use electrical tape, though that will probably come loose quicker than any other of the suggested methods in other replies.
Only the cable on the other side of the holdfast is doing anything.
Call a bike shop. Local prices vary on replacing the cables so I'd hate to hazard a guess. Even so, it's not much, and by letting them do it, they'll adjust the derailleur and correct any shifting issues as part of the deal. Assuming there aren't shifting issues that are being caused by something else.