Either soil moisture extreme can kill roots and result in leaf drop. So can cold temperatures. If the damage was too extreme or the conditions lasted too long the plant may not be able recover. However I would continue to expect it to come back. Wait until after the first hard freeze to cut the plant back to just above the soil line. Then over winter keep the plant in a semi protected area and keep the soil moist but not soggy. Next spring when the weather warms the new growth should resume.
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