普通人有多少存款，才可以靠利息生活？

This is the ideal case assumptions, just like the absolutely smooth ball on the absolutely smooth plane, described in middle school physical book.

Actually, personal wealth vanished to approximately zero occurred several times in the history, such as NK, Red Khmer, and so on.

So, we must make ourselves well prepared. There are several ways, but the least way is to save "enough" money, because it will turn to paper in some cases.