I have an Office365 subscription through my university. I believe what they are talking about in your link is cloud-only files (like collaborative documents, etc.). Personally, I almost never use collaborative or purely cloud-based documents at all, unless I absolutely have to (and even then it's usually through Google Drive). All my 'normal' work in all the Office applications is saved to local drives just like they always were and can be accessed without modification by OpenOffice, LibreOffice, etc. So even if my subscription were to lapse without my knowledge I wouldn't lose a single file. I do need to be more proactive in backing my files up to the cloud though (just some server space at my uni really) as my current back-up regime keeps 2 copies on different physical devices that are located in the same building which is not a good idea for fire and physical theft protection.