I also love my chickens way too much and I'm so sorry for your loss, my heart goes out to you. I'll be watching this thread hoping the other hen is found alive. I agree with the other posters about your hen needing some buddies. She won't be happy all alone. You can rebuild your flock, but with a negligent dog owner as a neighbor, you'll have to predator-proof your run and coop like Fort Knox. That's always a good idea anyway.
I too think you did the right thing about the dog. It's not really his fault, he was just doing what dogs do. It's the owner's fault. If they won't take the proper care and precautions for their dog, they shouldn't have him. Many people in your shoes just shoot the dog. I agree it's totally justified and often the chicken owners have no other choice, but it's too bad when the dog pays the price for their owner's negligence and the owners get off scott free. Animals don't know any better, people do. A negligent dog owner should be held responsible, financially and otherwise, for what they allow their dogs to do. But unfortunately that's easier said than done.
Again, I am very sorry for your loss, and please keep us posted on the missing hen and let us know how things play out with the dog owners.