Can't be of much help, but I also live in Georgia and have a Kwanzan
Cherry that also appears to be dying. Leaves started turning brown and
falling off in late July / early August. But there still seems to be
plenty of green in the branches.
My cherry is about 20 years old. I'm going to leave it in until next
year. I'm guessing it was the heat/drought earlier in the year that
stressed it out, and it's probably Mother Nature's way of surviving.
I'm going to give it a fertilizer boost in the winter and hope it comes
back in the spring.