An interesting thread. I'm a teacher and have been in this situation before. Have not had a morning break because I've been helping students then starving by lunchtime but eg a child is very upset and I need to talk to them to calm then down then go on lunch duty and so have no time for lunch. In those situations, I have been desperate for lunch.
However, I would never, ever leave a child of any age in the street or even in a school alone. I would be far too worried about what would happen to them.
As a teacher it's drummed into you that you're the teacher, social worker, nit watcher, counsellor,etc for children so they buck always stops with you.
I'd be having heart palpitations about leaving a child. I'd have been far more likely to take the kids with me and left you a note and called you.
However, I have taught in other countries and teachers are not trained like this. They believe that their job is to teach the lesson eg 2 hours and that's it. They're not going to do lunch duty, after school clubs, sport, counselling, etc. Their only job is to teach. I'm not saying if this is right or wrong, it's just different. So maybe this teacher was trained to think in this way.
I agree that the mum should have turned up on time but sometimes these things happen and our concern should always be with the child. In this situation the teacher obviously didn't feel responsible for the child.
Getting the teacher fired seems like a step too far. It would be better for the school to formalise what it does in these situations. In day care, for example, they wait for a certain period of time then call police and social services and your child is taken off with them.
Your daughter is ok which is the main thing and this is an opportunity for you to discuss with the school what should happen in future. This could help other children if the same thing was to happen again.