Nevertheless, because the chance of something like that happening is clearly higher than 0.0000000001%, Microsoft should simply never do such a drastic upgrade

Nevertheless, because the chance of something like that happening is clearly higher than 0.0000000001%, Microsoft should simply never do such a drastic upgrade automatically. (So, even within Windows 10, they should not automate all upgrades, because occasionally they will have to include bigger changes.) Also, users will not understand this, and will, rightly, blame Microsoft.