Answer: I don't think you killed your azaleas, especially if the overspray hit the foliage, but did not soak into the ground near the roots. The dead and otherwise affected leaves will fall off on their own so you won't need to do any pruning. It's a little late in the year to prune them anyway. Just rinse the plant off to get rid of any residual chemicals and allow the foliage to drop as it may. Rake up any fallen leaves and next spring, after flowering has finished, you can prune away any dead stems. (Next time you power wash, you can drape your shrubs with old sheets or blankets to keep overspray from damaging them.)
Best wishes with your landscape!
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