How can I restore the persistent data for Mac's native Stickies app?
Search for Stickies from the uppermost directory of your Mac (by navigating to Finder - Go - Computer or entering ⇧+⌘+C as a keyboard shortcut from Finder) and choose the directory Stickies at the bottom of the list from the screenshot.


In this directory there are rtfd files, from which you can view possibly all the contents that had been in the Stickies notes even though they have now disappeared when the Stickies App is opened. You can simply double-click them and typically they are opened in Rich Text Format by TextEdit App.