I feel for you. But the peony will live. It's just going into dormancy early. The only thing that it may do is starting to grow too early. Even if that is the case, your area does not get cold enough for any growths to die out. Anyway, this is a great opportunity to experiment and observe whether this early pruning has any beneficial effect to your plant. What I would do now is to provide complete shade for the peony. You just don't want to expose the peony to any more stress from being exposed to the hot sun. Would love to hear back next year of your peony's growth.
