JWs say that not everyone on the planet will get preached to, and the ones that don't are figured to be judged by Jehovah as unworthy, so don't worry about them.
Obviously not everyone will hear the Good News of God’s Kingdom before Armageddon and everyone destroyed at Armageddon will be destroyed eternally since it is Jehovah’s destruction.
Now here is an interesting question, how many will there be left at Armageddon? Most of mankind will probably die during the Great Tribulation and will still qualify for a resurrection. The world stage is being set for Global famine (peak oil, etc.) which Jehovah could use during the Great Tribulation to warehouse most of humankind. Those left (other than faithful Christians) will be those responsible for ruining the earth in a spiritual, moral and physical way and deserve destruction. This certainly fits the world leaders and those who put their hope in them (remember the mark of the beast?).