I have personally worked in buildings that had a "badge readers all stopped working for a while" problem. Fortunately, the badge readers only affected ingress and not egress, and only controlled exterior doors and labs; that's easily solved with a doorstop and a person checking badges. I can very easily imagine what could have happened in those buildings if a badge was required to leave a conference room.

And if you want to make that scenario terrifying, imagine being there on a weekend or holiday.

Grenfell Tower was "fireproof", and yet...

Power failure is a best case. I've observed firsthand cases of "badge access system went down, none of the doors open". That's less of a problem for external doors that allow people out but not in, because it can be solved by propping the door and posting a guard who checks badges. It's a massive problem when conference rooms and offices lock people in.

I just go up and over through the drop ceiling.

It took Milchick a lot more kicks than that to get out of the bathroom!