My prayers are with you. I am so sorry.
Our pastor gave a sermon once on caring for others. He said that we can do all we can to help another but humans have free will and make their own decisions. Your uncle chose to go out. Nothing you could have done would have prevented that unless you had a guard on him all the time and he would have hated that. He enjoyed his freedom.
God is taking care of him for you now. I hope you and his other angel can find comfort in that.
Anita, mom to Kat, 18, BP, lithium, topomax, risperdal, buspar