I’m trying to figure this out. When using Scrivener it will sometimes be unable to automatically save, and then it will close the document without being able to stop it. This seems very strange. If there isn’t enough room, why not stop saving and ask the user to clear some disk space? Instead it closes the document and loses everything since the previous save. It’s not like the application has run out of memory, because the application is still running.
It should be writing anything it couldn’t save into files, in your Documents folder within a special folder just for recovery files for this project. Is this not happening for you?
I suppose this reaction could be a problem if the project and the user folder are on the same boot volume—but, if the boot volume is so overloaded that programs can’t save a few bytes of text to them, that’s much bigger problem that should be solved post haste, and once and for all.