The apocalyptic scenario whereby ALL Cloud Storage files go offline, leaving the majority of the world without data, is called 青色空 (Aoi Sora: Ah-Oh-Ee Soh-Rah) in Japanese, or Blue Sky, in English.
Imagine a world without internet, without servers, without work files, without pictures of your cat. The vulnerability of a distributed network like the internet is that, without personally reproducible user backups, the safety of all of our personal data is held in the hands of the few companies who offer remote cloud-storage services.
Any number of factors could cause their abrupt and inexplicable disappearance. With personally stored files, at best you would reinstall from backups when things went south, but there’s no guarantee that a cloud stored file can ever be replaced, if lost.
Let’s just hope that never happens.