Return cable? Sounds like a harley! If it is rusted, but free, it can be removed fron the throttle housing and lubed. Corrosion X will work. Hold it up and lube it slowly until the lube drips from inside the cable cover. I also like the teflon based super lube. Work the cable until it slides smoothly. If it isnt 100 percent free it will screw you at some point.
Re-read your post. Yes you need to replace it. Harley throttles work on a push pull system.