Answer: It seems odd that an established butterfly bush would just suddenly quit. I wonder if the soil remained too wet over the winter months? In any case, I'd prune it back to within a few inches of the soil. This should shock it into growing new stems and foliage. If that doesn't do the trick in about 3 weeks, dig it up and replace it. Prior to replacing, amend the soil with some organic matter to facilitate good drainage.
Best wishes with your butterfly bush!
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