Your data does stay on your machine, unless you use OneDrive. The only other data stored there is settings, favorites, app info, and Start Screen arrangement so in case one needs to reinstall it auto loads via synch.I also do not like the Microsoft account. My data stays on my hard drives thank you very much.
It is wise to back up everything on an exterior drive. One may not have a current copy of a file, but at least one can keep working.I am lucky to have a fast connection but I do know what it is like when the network goes down. Happened to me at my old job, we were totally web based and when it crashed one day we had to revert to paper and pen. If I had not printed my work out I would have been screwed.