By writing "end of the world scenario" I mean that it happens so rarely that there is no need to prepare for that unless you are a prepper. I use a single bank

By writing "end of the world scenario" I mean that it happens so rarely that there is no need to prepare for that unless you are a prepper. I use a single bank for the last 15 years, there was no issue with it that would cause me to not be able to use my money. They usually have scheduler work during some weekend nights, and I don't remember any large scale issue besides that - for sure I didn't have a scenario where I was without money. For such scenario it is better to have some cash (which I do, but for other reasons - e.g. paying nanny or some workers that don't accept card payments).