Odds are you can simply grab the RD and pull it back out. If the cable is truly binding on a ride, but hasn't broken you can some save the day by stoppin g at a gas station and running a drop of oil or solvent into the rear housing loop.
BTW- on long (multi-day) tours I carry a 2" length of spoke in my emergency tool kit. In a pinch I can yank out the cable, and put the head into the adjuster and pinch the other end down to hold the RD in the gear of my choice. I can even manually shift between 2-3 via the adjusting barrel.
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FB
Chain-L site
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