If you draw a firearm with the intent to use it, you have employed deadly force. No shot needs to be fired.
If you use the firearm in self defense and a human being dies, you have committed a homicide--the taking of a human life by unnatural means, in which you were the agent of inflicting a lethal injury. You will find that in most State statutes, you will find a definition of Homicide.
You will also find statutes that resemble this: "Homicide--When Lawful"...
In other words, the law recognizes that there are instances when you may legally and morally employ deadly force to preserve your own life or limb, or to save you or another from the same or other maiming, crippling injury.
If you fail to report the homicide, you have now placed yourself in the realm of the offender. If the incident is reported right away, there are more than likely bits and pieces of evidence present to support your claim of self defense.
If you flee the scene, then you will more than likely be charged with Murder. This is the unlawful taking of life.
So, what do you do?
If I answer a call of "shots fired", and come on the scene to see you there, with a dead body, I will approach you, asking you to keep your hands where I can see them. I will disarm you, and read you the rights admonishment.
If there is OVERWHELMING evidence that you fired to save your life--or the life of another (children, wife, other innocent person), you might not even go to jail!
But remember this well--I (and other officers) are NOT the triers of fact in ANY instance. We simply observe, and determine if there is probable cause to believe that a criminal act has been/will be/is being committed. And, with a homicide, we have habeas corpus--literally, the body of the evidence--in the most literal sense of the phrase, laying right there. Thus, we have probable cause to effect an arrest.
You will more than likely be arrested, on SUSPICION of Homicide. What happens after that is up to the Court.
But, do NOT conceal or run away from the evidence. It only makes you look more like the criminal and less like the victim.
Hiding in plain sight...