Depending on the document, I do use the cloud for backup, but I don't depend on it as my sole backup. I use it primarily for saving things I find on the web.
I don't use OneDrive because I think it's clunky to use, and there are instances (as evidenced in this forum) that it is sometimes unstable--probably because developers were tweaking it behind the scenes. I don't like subscriptions, so I use pCloud. It gives you lifetime storage for one payment--just like a perpetual license. I've been using it for several years, and I never once had an occasion where my files mysteriously disappeared or I couldn't get access. It can be synchronized with your local drive too.
Whenever I create a new Word document and save it for the first time, a macro asks me if I want to revision it and whether I want to store revisions to my local drive, or to both it and pCloud. If I say yes, it creates a revision folder at those locations, and stores a copy of the document. It's useful when authoring because I can go back in time and retrieve an earlier work if I need to. After the document is finalized, I disable the revisioning flag, and delete the revision folder(s).
If one is working on an important document, they should be backing it up, the same as they should if using a master document. If they they are backing up files, they can always recover a corrupted document whether it be a single document or a master.
Yes, I use Zotero for citations too. It's not only free (I like free), but it also saves copies of the sources.