Yup, twist it back up and crimp it with one of those little end cap/covers. I'd bet the LBS would happily give you one. If it hasn't frayed far, I'd say there is still a chance you can reuse the cable if you ever need to. You'd need to trim off the frayed end, though. Then if there's enough cable left for reuse then it shouldn't be a problem. All depends on how bad it is now.