Frankly I cannot imagine any scenario within our lifetime (or beyond for that matter) in which a total nuclear disarmament was achieved. Unless it was replaced by a new kind of weapon with similar total destruction capabilities. There is no way in my view the big two nuclear nations would agree to permanently rid themselves of their nukes and become vulnerable to any nation or faction that somehow acquired them in the future. No way. Perhaps the likes of the UK and France, but good luck getting China, India, Pakistan or Israel to agree to ditch them.