Let me preface this by saying I've got nothing against owning a gun (I've got 3), but...
If you think carrying is going too protect in you in any way when someone else has a gun pointed in your face you're pretty sadly mistaken. Just give them what they want and hope your insurance covers you. Thinking you can Clint Eastwood your way out of a car jacking is a good way to end up with half a face. Even a dude with a knife at your back has a really significant advantage over you if you're carrying. Personally I think carrying just makes people feel safer, it really doesn't contribute to actually being safer.
I guess it might be useful if you're positive the dude is going to kill you anyway (at least you get to roll the dice), but your chances of killing him are terrible if he got the drop on you. And if he doesn't have the drop on you how do you know he's planning to kill you?
I'd say forget the concealed carry and go learn aikido. Still not a good chance of survival, but in close quarters it'll serve you better than something you have to extract from between your balls or off your ankle.