Since you live in NYC and "things" seem to happen there, and since your child is a priority, maybe you and your wife could start a new habit: as soon as she's picked up the child, text you that fact, every day, every time. If something happens and you haven't received that message, you'll know what you need to do next. This time, the time factor allowed you to assume (correctly) that the child was picked up. What if the incident had happened very close to pickup time?

As was pointed out, briefcases are a nuisance. You might bring in an empty backpack and leave it in a desk drawer. In case of evacuation, just dump the contents of your briefcase into the backpack and go.

Blast's baby sling is a superb idea. You might even be able to wear it under your backpack. Pack in back, baby in front.

Re: the fire alarm. Most buildings have fire alarm triggers on all floors. If everyone else has forgotten, couldn't you trigger the alarm on the way out?

If you have weekly/monthly meetings, you might ask why the company's emergency procedures failed so badly. Make suggestions. One could be to label where the various stairs go.

Did you suggest to anyone besides your friend to take the stairs? If not, why not?

Overall, I think you did a reasonably good job. You would have gotten more points if you hadn't forgotten your kit, but I suspect that won't happen again. Like they say, we learn more from our mistakes.

Sue