jazZRo took the words off my keyboard. I was going to suggest looking at what Mashable do in a responsive view to see what their solution is.
I have recently spotted a clever alternative that Apple (http://www.apple.com/) have done - note you should open this on a mobile device to view it properly - where they still keep all the top level items but you can rotate through them all without having to re-structure the nav.
As an alternative to the high level, the site for the Rugby world cup uses a collapsible sidebar (Microsoft Azure uses this for their navigation where each item opens another item next to it)
I think their argument would fall under the lines of when a user is focusing on the nav, the rest of the page becomes less important.