Realistically, if you think you can draw from concealment and shoot the assailant before he shoots you, prove it with airsoft. Typical draw-to-fire times I'm seeing in training are around 2-3 seconds. The guy who already has his shirt swept back and is waiting for the buzzer and is playing a twitch-game (instead of real life) can get the draw out in around a sec or so. The BG can shoot you multiple times before you're in the game.
How to deal with an armed victim
'Sup y'all. Lately, seems like more people are carrying handguns. Sooner or later, we're going to have the situation where the punk you're taking down is armed with somethin.' So I'm making it a Best Business Practice to tell the punk to pull off his pants first. That's for my safety. If he decides to go for his piece, I'm gonna drop him.