I believe my game plan would be to stay put, with the gun still aimed at the guy. To be at my car, he's in the garage of my house, so his only way out would be through me. I'd verbalize any movement in my direction will be considered a threat and I will shoot. The guy either stays in the car until the cops show up or tries to come through me to escape, and I shoot.
Another poster willing to kill to protect property. Amazing and a more than a little scary.