Obviously, none of us know for certain if Apple will kill off the iPod nano in the near future. I can definitely see Apple going down to 2 iPods: iPod Touch & iPod Shuffle. There is always a slim chance that Apple will address the iPod in the October 2014 keynote, but it is highly unlikely. If you are looking to update, now is a good time. It is extremely unlikely we will see them planning any updates or discontinuations of the iPod nano until at least next September.
If you would rather wait, buy the iPod nano a few days before next year's September keynote, you have 14 days to return, so if they update, just exchange for the newer gen iPod, if they discontinue it, at least you will have secured one of the last ones.