We made our little boy give Grandad all of his dummies. And with a little added distraction of chocolate it was a success. 
I carried him round as he was falling asleep and he didn't mention his dummy until five am. I said Grandad had them and he remembered. Tonight may be different. Sleeping with his mouth open did give him a sore/ dry throat. But I suspect he slept better being able to breathe. So hopefully the next phase is having him sleep through.