Interestingly, on the 195 I'm travelling on right now, there's no mention of staff instructions at all. In fact, the word staff doesn't appear once.Breaking it down a bit - the Guard not patrolling with a broken PA is pretty poor - although as you yourself conceded the guard was apparently oblivious to the faulty nature of the PA. I can’t see where the railway has breached the rules it’s trying to enforce here?
Coming to the notices I refer to - they’re all worded slightly different but typically it just says to await instructions from staff. It doesn’t put a time limit on it. It doesn’t even say it has to be the on train staff. It just says wait. If your life is in immediate danger you will be acutely aware of that fact - up until that point you are always safer on the train - even in any of the scenarios listed above.
All it says is "In most situations it is safest to remain on the train," and, "if required, self evacuate." (I'm paraphrasing slightly.) Only AFTER I have self evacuated from the train does it say I should listen for instructions.
On the thing about the PA, it's a peculiar one because I would assume that, if it is working correctly, the guard would be able to hear it from his cab? In which case you would hope that, particularly in a situation like yesterday, standing instructions would be to go and talk to your passengers. It's a tough one and, yes, I'm giving him the benefit of the doubt that he genuinely didn't know - but I'm not convinced I should be tbh. It really was very, very poor.
Edit: photo of a Class 195 safety poster: