How was he threatening you? If he said he was going to ''kill'' you then drawing would be your next course of action. I would have told my friend to get on the phone with 911 right then and there. I'm sure if they would've called first and the police arrived on the scene things might have went better.
I always carry my permit as it's the law where I live. I don't know why you didn't have your CCP on you I don't think anybody on here leaves the house with out theirs. I keep mine in my wallet and never leave the house with out it as it has my Driver's license in it which I also need with me at all times when I carry.
In conclusion, I would've called the cops told them what was going on and that I have a permit to carry and if he kept coming or grabbed a weapon I would've told him not to move til the police arrive. If he kept coming I would've pulled the trigger and asked the gas station attendant if what happened was on tape so it could be used as evidence and told my friends to stick around as witnesses.
I'm 21, some people may think I'm dumb or a ''thug'' but my safety is a number 1 priority. Like others have said I'd rather be in debt or in jail then dead. Also, I have no experience in hand to hand combat or karate like the OP states. If he really has all this training why would you have pulled your pistol? Sounds like your lazy in wanting to deliver a good as whooping or you wanted to show off for somebody.
Where do you live that the cops are that bent? A convicted felon wins out in words when he has a history of this? You must be saying the wrong thing.
Sic vis pacem, para bellum