I’m beyond delighted to announce that Oliver came back Sunday evening! I had spent all afternoon going around my neighborhood calling him. Got in my car to go see my parents and when I got back and parked I heard this familiar meow and there he was. I was SOOOOOO happy to see him. The other outside cats I feed seemed glad to see him too. There was a lot of rubbing going on ;-). He was really thirsty which leads me to suspect that he was probably trapped somewhere and maybe hearing me and his desperation (last time I had seen him was Thursday morning) motivated him enough to get out or to meow enough that someone got him out. He looks fine and was eating fine.
One more success story to give hope that those felines can return even after days have gone by.