To quote Capt. Kirk ... "He's dead Jim".

You will never get a satisfactory tree out of it, because the new branches are going to be very weak.

Remove tree and start over with one better suited for the Tucson climate, including the occasional hard freeze.

I second that ... ours froze all the way back to the trunk, and I have yet to see a green one in our neighborhood. I replaced ours with a native that can handle the climate AND uses less water AND is more wildlife-friendly. Everything happens for a reason!

Trees for Tucson doesn't offer this species anymore, as it's too "thirsty" for the desert. Too bad, it's a really nice tree and I really liked ours before it froze.

Here is a link that might be useful: Stressed Trees Spark Planting Shift

Thanks for your responses. It helped me tremendously. The tree is coming down tomorrow.