Yes, a hand-gun ban would leave a sufficient means of self-defense in Washington DC, because people have many other options available to them. People can use stun guns; people can use pepper spray. Shot guns are also a popular option. So is calling law enforcement. Guns are not necessary for self-defense in DC.
Having a hand-gun ban still leaves others with a means of self defense. It does not prevent us from learning self defense, or carrying a knife for protection. Despite thinking it will leave us with a means of defense though, I do not necessarily agree with banning hand-guns. They are not the problem, people are.