Put the collar back on and play the waiting game with him. You'll win!! I've never met a cat that didn't object when they were first forced to wear a collar, but they get used to it in no time. He hasn't had one on in a while, so it looks like you're starting from scratch. I'd also get a break-away collar in case he does get out and maybe gets hung up in some shrubs or the like. That way at least he isn't going to strangle and the collar will come open as he pulls on it.