There is little doubt in what I would do. The bad guy has drawn a gun and has made a threat to inflict bodily harm and I would take the necessary action, to include deadly force, to remove/end the threat.
Under the Florida "Castle Doctrine" the premises that are covered (abode only, or other places too), what degree of retreat or non-deadly resistance is required before deadly force can be used, etc.
Typical conditions that apply to some Castle Doctrine laws:
An intruder must be making (or have made) an attempt to unlawfully or forcibly enter an occupied residence, business or vehicle.
The intruder must be acting unlawfully—for example, the Castle Doctrine does not give the right to use force against officers of the law acting in the course of their legal duties.
The occupant(s) of the home must reasonably believe the intruder intends to inflict serious bodily harm or death upon an occupant of the home.
The occupant(s) of the home must not have provoked or instigated an intrusion, or provoked or instigated an intruder to threaten or use deadly force.
In all cases, the occupant(s) of the home must be there legally, must not be fugitives from the law or aiding or abetting another person in being a fugitive from the law, and must not use force upon an officer of the law performing a legal duty.
IMO, the best part of the law is that it allows a person(victim) to stand his/her ground.