Caleb, this is such a sad story, and I'm so sorry to hear about your family's loss. Your brother should be honored for his service to our beautiful country.
I took a survival class this past spring and the Search and Rescue instructor told us several stories just like your brother's. Hypothermia is the number one killer in the wilderness... We also learned that communication with loved ones about our location and expected return is the number one lifesaver. I hope we can all listen to stories like your brother's and learn from them...