I am sorry to read of what you are coping with / enduring. By the words you wrote in your post you can easily realize just how much you truly love your lad "Odie."
I have a few bits of good information to relay to you that you may find of comfort.
My ex-fiance back in the year 2000, had a cat named "Peanut." "Peanut" was an indoor cat, who never, not ever, went outside as she and my ex lived in the Laurel Canyon area of Los Angeles, which is hilly and covered with trees and scrub brush etc., and is known for having many coyotes.
"Peanut" ran away one night and disappeared. We would go out looking for her each day and night. And late at night we would run into coyotes on the streets. We saw many of them again and again and again. And it seemed the odds were next to impossible that "Peanut" somehow survived. But she did.
Three weeks later my ex found "Peanut" in a house that was being constructed at the bottom of the hill below her house. Somehow "Peanut had managed to adapt and survive."
As you may know - a dogs average life in the wild is 10 years. This applies to mid-size dogs, which your "Odie" appears to be. That is how long feral / wild dogs in the wilderness survive, including in areas with known, larger / natural predators. Dingo's in Australia are not that large, but are know to live in the outback for around 10 years. And Australia is known for being one of the most dangerous wooded areas in the World.
As I write this there is a feral rescue kitten (that I am fostering named "KID") laying on my lap, he has with two coyote bites (nips) on the rear of his neck and his back left hind quarters (which required surgical staples to close.) His Mother (a feral cat named "Mom-Cat" for all the litters she had over the years here in our neighborhood) and his Father ("Blackie") and KID's older friend cat "Cherry") and his neighbor cat across the street ("Fleas") were all attacked and taken by coyotes in the month of July 2019 here. This little kitten somehow not only survived the attacks mentioned above, but relocated successfully a block away from the attacks which was nearer to my office.
So in keeping with the above, your "Odie" might still be okay.
The other possibility relates to the following - I know many feral / stray rescue volunteers. For both dogs and cats. And I and they have met many people who have adopted pets, that had runaway or in some case started to take care of a dog or cat, because the dog or cat chose to start hanging out at their home vs. that of their owners. One pet I knew shared two families. They would go back and forth to both families as if it was like joint-custody with a child.
Unfortunately, or at times fortunately (if an animal is being abused or neglected) a new pet parent may not even reveal that they are taking care of and may have rescued then adopted a runaway pet. Because they are lonely, at times is the reason. Think about it, a lonely person is driving, comes across a dog and just picks them up and takes them away. It happens all the time. Not all people are honest. Not all are going to run chips to try and find the parent. They rationalize in their heads "Oh well, they were not taking care of their dog so I will!"
So if "Odie" felt it was necessary? in order to survive? to be friendly with a complete stranger, "Odie" may have been rescued and adopted. Again, it happens all the time. In this case, hopefully this individual will see one of your flyers that you made and come forward and contact you. I hope that occurs shortly.
Please don't give up hope. It is very admirable that you have put your heart and energy and efforts into the search for "Odie" and that for many years you provided "Odie" with a loving, kind, affectionate and comfortable home. That means a great deal. All pups should be so blessed and fortunate.
My kindest regards,