Sorry to hear that, john_in_nc111. Continue watering to achieve 'constant' soil moisture as best as you can and maintain 3-4" of mulch. Then observe what the plant does. Does it leaf out some more and from different places? Etc? Do not fertilize as this may stress out the plant some more. Try not to overwater.

If unsure whether or not to water, insert a finger into the soil to a depth of 3-4" and water when it feels almost dry. Make a note on a wall calendar every time that you water. Do this daily for 1-2 weeks. Then review the information on the calendar and determine how often you watered. Set your sprinkler or irrigation to water the same amt of water (1g/2g/etc) on the same frequency (every 2/3/4/5/etc days). Re-check using the finger method if the temps change 10-15 degrees and stay there. Remember to water during winters too when the plant is dormant but it is dry and the soil does not freeze.

You could then prune the dried out section in 1-2" increments and stop when you get to parts that are still alive. But, I would rather wait until the spring to prune out decidedly dried out sections.

As you noticed, the roots may be ok and it may grow from the bottom again. But there could other areas from the 8' tree where it might also leaf out. Wish those blue flash lights used in CSI Episodes would tell us that.

Finally, determine what caused the lack of moisture ("operator error", forgot to turn 'on' the sprinkler, etc) and then appropriate steps to prevent the problem in the future.