Answer: It's really difficult to diagnose a plant problem without seeing it, but I will offer a possibliltiy - rock rose is susceptible to root rot if the soil doesn't drain well. I'd also check for spidermites. These tiny insects feed on the foliage and cause a withering, stippled appearance. Continue to prune away the affected plant parts (in case of spidermites). Next spring, if the roots are healthy, they will develop healthy new stems and foliage.
Best wishes with your rock roses!
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