There will be a big red switch somewhere to cut all power in the event of (for instance) a fire. This will bring all power down in an uncontrolled manner leading to all sorts of bad stuff.
I'm not an IT wizzkid, more a dinosaur. Please excuse: but as an engineer/pilot of sorts I would like to think that in the event of having to evacuate and switch off a working system, by a 'kill switch' it would not be harmful and uncontrolled. The expectation would be that it would be used again after the emergency. Why do you say it would not be protected and "lead to all sorts of bad stuff."? Back to the topic, before this becomes an IT classroom, why would BA have a system that was so vulnerable to an emergency shutdown?