By statute and case law, the public draw of a firearm represents "force" and not "lethal force". The standard by which such use of force is warranted is different for the two. Only if you discharge the firearm, does it become "lethal force". Even into the air, or the ground. So "firing a warning shot" is definately out.
Obviously, whether or not your life is easy depends on the circumstances and the individual district attorney.
In my particular case, it was to stop the imminent assault by 5 individuals while waiting at an ATM. I reported the incident, and just had to fill out a statement form. [ with consent of my lawyer of course ] To my knowledge, none of the individuals came forward or were found.