I think you meant CHICAGO and DC Seagoon? AFAIK, in NYC it is still legal (although very difficult) to own a handgun.
And while those bans in Chicago and DC have stood so far, I dont think they have been seriously challenged, and I also believe they grandfathered in anyone who already lived in the city limits and legally owned a registered handgun. You just couldnt bring in any more. If someone could correct me if I'm wrong there?
SF is saying if you are a legal, registered handgun owner, you have until April (I think) to turn them in. That wont fly. You cannot force someone who legally owns and registers a handgun to turn it over to the govt. when you pass a law after the fact. If they had grandfathered all existing owners, there wouldnt be a legal leg to stand on (well, other than the 2nd amendment, but thats already been trampled) to prevent new handgun sales or registrations. They cant just declare guns already legally registered as suddenly illegal. Even California law precedent is against them.