That's just not true. Most ATMs still run on Windows. There is a lot of industrial machinery running Windows 98 or XP to this day. A lot of POS devices too. Almost all accounting is done on Windows. The amount of chaos if it disappeared would be immense, it would probably be on the same order of magnitude as the last pandemic in terms of immediate economic impact as businesses have to manically switch to alternatives, and hundreds or thousands of people would die from financial chaos alone. Linux is probably still worse because it would mean that more than half of smartphones are suddenly bricked, literally all of the internet just stops working, and a shitton of industrial automation stuff is gone.