Q.Acer Die Back
BushDoctor provided an answer for my question. More information: the branches split around 3 feet from the ground. One is living and one is dead.
Certified GKH Gardening Expert
This is helpful! It appears to be Verticillium Wilt. This disease is not curable, but can be maintained with quite a bit of effort.
Here are some articles that will help:
https://www.gardeningknowhow.com/plant-problems/disease/verticillium-wilt-treatment.htm
https://www.gardeningknowhow.com/ornamental/trees/japanese-maple/japanese-maple-tree-lifespan.htm
https://www.gardeningknowhow.com/ornamental/trees/japanese-maple/japanese-maple-problems.htm