Not saved but given the possibility of a so called "second chance". JWs explain this about the hope of resurrection of previous dead people who did not hear the Christian message by saying that Jehovah will give them a chance to hear it during the millenium, that's kind of a "first chance". Then they"ll be zapped and killed again forever if they don't obey rules during the millenium.
The "second chance" is when someone in the present is thought by Jehovah as not having been exposed enough to His "witnesses" glorious message so He gives them a "second chance" by being resurrected in the Millenium. If they don't like the Lion petting routine, zap! Even if they do they still have until the end of the Millenium to go through another test with Satan brought up for an anticlimactic and boring sequel to Armageddon.
So, if every one in the world is nuked like you said most of them, at Jehovah's pleasure, should pop up out of the ground for what could be called a conditional salvation. But if that nuclear war were to happen killing off everyone on earth, as you said, then it would contradict a whole bunch of other Watchtower BS that would make the isssue moot.