When faced with a firearm or a knife, any self respecting martial artist will tell you the one technique that will save your life.

Running the fuck away and or taking cover.

When it comes to hand to hand combat, understanding the dynamics of how to protect yourself and control the opposer like in Jiu Jitsu is very useful and can also potentially save your life.

But no, if they have a weapon of any kind, get the fuck out of there.