My understanding is that IF the court sides with the city on the current lawsuit, then anyone caught possessing a handgun or selling ammunition or etc. would be arrested on those charges and sent to jail for up to six months and/or fined upto $1000.
What the chances of a violator being caught are, I don't know. Of course, if one defends oneself with a gun, they would likely be busted.
I guess that if the city wins the lawsuit, they will start enforcing the law immediately. In either case, an appeal seems probable.