It's incredibly rare for multiple AZs to go down at once, especially since they are more than a few miles apart from each other.
> Each Availability Zone is separated by a meaningful physical distance from other zones to avoid correlated failure scenarios due to environmental hazards like fires, floods, and tornadoes.
https://docs.aws.amazon.com/wellarchitected/latest/reliabili...
Very much so - Australia only got a second region this year, so if your work required data to remain in Australia, you just had to hope that ap-southeast-2 didn't have a major issues. I'm sure there are plenty of other countries with only a single region.
If I have to think too hard and do too much work about how I lay applications out, I might as well just rent in a colo.