Unless he takes it away from you before you know he's there. Martial arts training can't be taken and used against you.
Unless your opponent is also a martial arts expert, and is physically much superior to you. A gun is an equalizer, and you don't have to make physical contact to use it.
Don't take this the wrong way. I got nothing against martial arts. It's a great thing to know, teaches discipline, and physical conditioning. In a really desperate situation, I'd rather have a firearm.

