Incase some may not know, you can always restore a page to a previous edit. So if someone just decides to make your entire page blank, you can just click the arrow beside the edit button and scroll down to the history button. From there, you can choose to restore the entire page to any previous version.
Users, registered or not, also cannot delete any pages. Only the admin (Yumei) may do so. Though if you're the paranoid type, just go ahead and copy+paste the source version of a page and save it as a notepad file.