Do the deleting notes and notebooks, really deleted?

When I delete note or notebook from Joplin, do the notes really deleted themself from the server itself?

Let's be correct in WebDAV and OneDrive the notes is not deleted as file completely? Why?
Why to save notes and notebook in server as file .md?
So do really my notes is deleted in Joplin cloud? Can I be sure for this?

It depends on your note history settings. That allows you to recover data (revisions + deletions) until that limit passes, then the data is deleted.