[happytoexplain]

I see this attitude a lot, and it drives me a little crazy. All the conversations I've heard between developers and project managers immediately spring into my head. "But what if X happens", "Well, we showed them a message about it. There's nothing else we can do." This only makes sense for confirmations ("Leave this page? You'll lose your work."), and only sometimes. In most other cases, it's just an excuse to keep things simple for developers. Software can do anything you want, especially if you own the stack in question - you just have to care enough to design and pursue it. There is always an at-least-pretty-decent UX answer to any problem. In this case, some off-the-top-of-my-head possibilities are simply disabling writes, or showing a message with better wording at write time in Explorer, e.g. "This file will be deleted . . .". If a designer takes the time to think about it, they could come up many more, perhaps better, possibilities.

Hell, even just changing the terrible wording on the notification (and putting it somewhere much less ignorable) would be a step forward. E.g. "Your files have been temporarily moved to X. Any files you place in My Documents, My Pictures (etc) will be deleted when you log off or turn off your computer.").