Answer: A rose bush that has been established for 20 years will certainly suffer from transplant shock when dug and moved; compounding this will be the stress of being replanted in the summertime when the temperatures are high and the sunshine is strong. Although we don't always have a choice in theses matters, winter, when the rose shrub is dormant is the very best time to transplant.
You did the right thing in pruning the shrub down. Doing so will encourage the development of healthy new stems and leaves. All you can do at this point is keep it well watered and wait. As soon as the roots establish themselves, you should see new growth. Best wishes with your rose bush!
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