Disclosure first - we're a Microsoft partner and MSP and support lots of users at customer sites.
We've seen ONE occurrence of data loss from Windows 10 upgrades. And that user, when we diagnosed the event after the fact, admitted that he'd seen a prompt to do something, clicked one of the buttons and hadn't actually read the message. He also said that "yeah, it warned me a couple of times that it was going to do something" (as in delete his apps and data), but he clicked yes to proceed.
Personal opinion - it's going to be hard to make MS liable when the user is warned what is going to happen but continues anyway without a backup. Or, in this case, not storing documents on the server shares like he'd been told to do for many months.
Just about every software package or app used will eventually go through an upgrade. Making software companies liable for all mistakes that users can make will result in significant cost increases to cover the required insurance.