As others have said, my personal policy and the policy I recommend to others is to call the police immediately if you have to display your pistol. Notice I said display, not merely get my hand on it under my shirt or suit coat. Even then it might be prudent to call the police, if or in case someone saw you make that provocative move. You want to be the first person relating the facts to the police.
In all candor, there is a danger in this, if the facts you relate to the police do not support the use or threat to use deadly force. I realize the original post was a Reader's Digest condensed version of the facts, but on that little information, I think your friend might have a problem, if this incident is reported to the police as described. As others have said, I didn't get the feeling that he "reasonably believed that deadly force was immediately necessary to prevent the other's use of unlawful deadly force." However, the threat of deadly force under TPC §9.04 may have been justified. If so, I believe it would be a close call and very possibly one to be made by a jury. Not being able to identify what was in the "attacker's" hand cuts two ways and a good trial lawyer, whether prosecutor or defense attorney, can get some mileage out of it.
Now, let me take off my lawyer hat and put on my instructor/teacher/perennial-student hat. I would never support a change in Texas law to require more training, or more frequent qualification, to obtain or renew a CHL. However, anyone serious enough about self-defense to get a CHL and carry a gun should dedicate a reasonable amount of time and money to get training and to practice! The greater your skill level, the longer you can delay deploying a firearm and still be able to defend yourself. Equally important is the fact that you will better understand when it's time to push the "GO" button and how to go about it. There are be tactical reasons why leaving a vehicle would be prudent, but they are rare. There are also factual/legal ramifications for leaving a vehicle to point a gun at someone, not the least of which is how as rookie prosecutor, grand jury, or trial jury are going to interpret such actions.
I occasionally tell a story about myself that helps to explain why I stress that training and practice can save not only your life, it can help you avoid having to injure or kill someone the law allows you to shoot. I don't want to tell it in a forum open to the entire world, but suffice it to say that there is a man alive today solely because I had sufficient confidence in my shooting skills to delay taking a shot. The shooting would have been justified, but he would have died for a relatively minor infraction and I would have been second-guessing myself for years.
Learn the law, not just by reading the Penal Code, but learn also how it works in the real world. Then get training and practice what you're taught; not once or twice a year, but on a regular basis. I tell my students that completing any class or course does not equate to mastering the skills and concepts presented. The most an instructor can do is teach you what you need to learn and master by practice. And this doesn't apply only to the neophyte, it applies to all of us. As Gregg Garrett, owner of Comp-Tac said in the excellent seminar he gave at the 2007 TexasCHLforum Day at PSC, "the mark of a good instructor is that they always consider themselves lifelong students." Gregg is a very wise man and we'd all do well to heed his message.
[Oops, how did I get up on this soapbox -- again!?]
Chas.