As a last resort, you can fight the shooter. This is best as a group, but still possible as a solo endeavor.
Your main goal is to disarm the shooter. Improvise with whatever weapons are available; hit them with a fire extinguisher (the most effective), charge at them with a chair to knock them down, throw glassware at them, etc. Whatever you choose to do, commit to your actions. The slightest hesitation could result in death. Remember, your life depends on it.
