This is a tough, but good, question. I honestly would probably retreat. Unless it was in my home. If I was at work, elsewhere I currently carry a firearm for my job so this is purely hypothetical, I would retreat. In my own home, I would shoot. I feel that more than just my immediate physical safety is breached when someone forces their way into my domicile. It brings with it a dis-ease that cannot be relieved very easily.
"You can all go to hell, I'm going to Texas."
---Colonel David Crockett