This morning, Harry was back in the yard, after three days of being gone! He seemed a little thin, but wasn't immediately hungry. Nor was he filthy dirty or hurt.
My best guess: Harry ran off to play in the woods and get the smell of shampoo off of him. It started raining, and he took shelter under someone's porch, carport, etc. Whoever it was saw a dog with mange and no collar, and took him in, explaining why he's not starving nor dirty. It probably took him three days to escape, but Harry is a real escape artist, so they couldn't hold him forever.
Here's the new mood in my house this morning: