Dogs do not "go off to die," states dog expert Kelly Dunbar of Dog Star Daily. Dogs that don't come home either got hit by a car, were stolen or got lost. Many end up in the local animal shelters.
Dunbar cites two stories of old dogs whose owners presumed they had "gone off to die" but the dogs, very much alive, ended up animal shelters and were put up for adoption.
Older dogs often suffer from sensory deficits such as decreased visual acuity and hearing. They are more likely than younger dogs to get lost. They also suffer from decreased mobility and are more likely than younger dogs to get stuck in landscape features such as ditches and not be able to make it home. The American Kennel Club recommends that owners take their aging dogs to a veterinarian for an annual or even semi-annual checkup.