Rather judged by 12 than carried by 6, as the saying goes. Unfortunately, my gun is in the car.
But I never go anywhere where I'm not aware of multiple escape routes if available, "safe areas," etc.
If a gunman were to be firing shots at the end of my hall, I'd use the small mirror in my desk to get a view of whats going on in the hall. Depending on his location, I'd do the following:
1) If he's coming down this hall and not the one that runs perpendicular to it, I'd barricade myself into my office. The offices here have solid wood doors on them, and are very stout. I have enough furniture that could easily be moved in front of the door, effectively keeping the shooter outside. I'd then get behind the oak desk I sit at and take the opportunity to call 911 and corporate security.
2) If he's heading down the other hall, I'd exit the end of the corridor and head to my car. I'd be down there in less than 20 seconds and retrieving my Glock. Then I'd make my way back up, making sure to not to get caught unaware coming back to take the guy out, and when I came across him I'd do my damndest to send him to be judged by God. I'd probably be fired and arrested, but I'd be alive and my kids would still have their dad.
God Bless Texas