Board Thread:Boruto Discussions/@comment-25319479-20160502145551/@comment-3279282-20160503130254

OrganicDinosaur explained that already:

Older Kawaki: 「お前も七代目と同じ所へ送ってやるよ…ボルト」

"I'll even send you off to the same place as the Nanadaime Hokage...Boruto"

[T/N: 送ってやる Can also mean 'to bury' (ie. an alternate translation for this line could be like, 'You will also be buried at the same site as the Nanadaime Hokage'). Kawaki is lightly implying that he's going to kill Boruto, in other words. So there is some implication that either Naruto is dead, or in near-death offscreen. The wording is unlikely to mean he's just off somewhere else].