Of course it isn't truly gone-- that's true for anything on the internet. You could make a bunch of nasty posts here on AD, have a change of heart and go delete them all. They're still out there if you use the cached pages or the wayback machine.
That is why many people say to think twice before you post or put something on the internet (shades of "would you want your MOTHER to see this?").
By now it may be deleted from Facebook servers- or at least deleted from visible view. If somebody is that bored enough or determined enough they'll go digging in the internet to find it. So I wouldn't worry that much about it.
Here is the info (you are right AlleyCat- I think it's fairly new.. within the last year or so)-
https://www.facebook.com/help/224562897555674
and if you click on the link in that article it does take you to the Delete My Account page. I think normally you have to go through Settings>Security>Deactivate my account-- there you are given the choice of deactivating ('putting account on hold') or deleting permanently)
