My DS just 4 and my DD 2 both had a dummy at night and nightime only but both were obsessed! My DS would talk about needing 'dodie' like a true addict, we got them both to choose a toy they both really wanted and asked them to give up the dummy!
DS did the odd night before preceding to hide a stash in his cabin bed! DD wailed when she realised it was gone then suddenly one night we said 'right the time has come to put them all in the bin' we made a big ceremony out of them both throwing them in the bin with lots of 'yuks' and 'dirty's. The 1st night DS was beside himself for 10 mins so I lay with him, he's never mentioned it since that night, two weeks ago now. DD was fine the 1st night then struggled the 2nd and 3rd night so we lay with her 5 mins then its been fine since! We now have the toys they chose to buy though. Phew what a relief potty training next, good luck to anyone else about to ditch the dummy