For me personally, if I'm carrying, I've already made the decision to put my life on the line to defend others. What I do will depend on the situation, but it won't be turning tail and getting out of dodge. I've been through training with active/retired LEO and military and when they talk through scenarios, they don't always agree with each other or have all the answers. There are no absolutes when it comes to this (and hopefully it never will), but in my opinion the best thing you can do if you have made this decision/commitment is to practice/train and think through the different scenarios. When the SHTF, you'll start running on instinct and learned behavior...
For me personally, I've already made the decision to put my life on the line for myself, my family, my friends and neighbors.
Strangers on the other hand is a completely different story. I am not paid to defend strangers, that's the police's job.
And my family and friends would be pretty upset with me if I got wasted while playing cop for strangers.
Additionally I don't wear a bullet proof vest, I don't have radio backup, and I don't have a tactical rifle nor do I want one.
I believe that if you are armed and you are accosted, then you stand a very good chance of winning the fight based on several factors in your favor if you are properly trained and have recently drilled. Every 3 to 6 months is a good drill interval to keep your training and reflexes sharp.
But as far as a situation like in the video, where a shooter has prepared himself to go on a rampage, in that case your chances are less than 50%, which is not good odds.