1. How to delete pages
If enabled (see HelpOnConfiguration and HelpMiscellaneous/FrequentlyAskedQuestions) and allow by ACLs, you can delete pages with the DeletePage action. Note that deleting means to make a backup copy of the page, and then deleting the page file. This is almost like saving an empty page (which is not allowed by the system).
What this means is that you can get back at deleted pages by using the standard mechanisms, see also the HelpMiscellaneous/FrequentlyAskedQuestions entry "Can I restore a page from an older version?" for this. Especially, if you enter the page name into the GoTo dialog, you'll see the usual page creation stuff, but clicking on PageInfo will reveal the old version history, unless the page was purged out of existence inbetween.
The only way to unrevertably and completely delete a page (including backups, history, attachments, etc.) is via the shell on the host system. The page files are found in the "data/pages/<PageName>" directory, and you can simply delete the whole <PageName> directory - no way back in that case.