Glad you got out okay, you're in a bad situation in a car, it means you're close enough for the other guy to take your gun very quickly, and you're not free to move. Also that close you're at real risk of knife attack.
If your standing in the open, and the other guy is 20 or more feet off or there's a car or something keeping him away, then I would give him the chance to run.
If there's nothing keeping him off of me, or he's armed with a weapon, then I'm pulling the trigger.
Now a little legal advise. If you are going to use any type of self defense, then erase the word KILL from your vocabulary. The objective of any type of self defense is to STOP or PREVENT the, for lack of a better term, "bad guy" from hurting you or anyone else.
If you carry a gun, take the time and money to get training, both in how to use the gun for self defense, and in some type of martial art or unarmed self defense class. You may very well find yourself in a situation where your gun is not available.
And make sure your chosen training deals with defense against guns and knives, they may take yours away.