To an extent it is. If you have your file stored in OneDrive, and your physical hard drive dies on my local computer, you have a copy safe in the cloud. Also, if you have the file in OneDrive and you make a change and save it. Then later make another change and save it. And then decide, I really wish I wouldn't have saved those changes, you have revision history and can go back to that file at a previous point in time.
That's actually not the way it works. I
f you let your subscription lapse, you get 30 days in full read/write mode and don't lose any of your files. You can even create new files.
For the next 90 days, your data goes into a read-only format. You can view and download any files you want during this period, but you cannot edit files, nor can you create new files. If you have more than 5GB of files (the free space limit), syncing stops.
If after 6 months you haven't removed your data, Microsoft will permanently delete the excess over 5GB (Free account limit). Since that data is no longer being synced, it will remain on your machine.
The best plan is that when you decide to not renew, is to unlink your local computer as quickly as possible thus not giving onedrive any chance of touching anything.