It appears to have gone away by Pages v5, during the features purge. You need to either use an old version, or get used to hitting ⌘ + R for rulers each time you make a document (or use the menu with the mouse).
You can't with the new Pages versions. Even creating a template with rulers included will not work. Likewise with thumbnail views and the newer page zoom view, all have to be reset each time you create a new document. Apple continues to improve Pages so maybe we will see that in a future version.