They died already. However they died before hearing the GOSPEL preached. they heard it preached and hell was emptied. And HE took back the keys to hades and death.
That will not happen agsin
HE will not descend again to preach to the dead Which is why THE GOSPEL is for the living and preached to the living until the year of HIS FAVOR is complete
All will physically die once but not all will suffer the second death
The first death is a spiritual death. Not one human being who woke up in the first Earth understood what the voice of God was. Without hearing the voice of God and obeying all his commandments like all the former prophets and saints did and forced to obey, you're spiritually dead until after your second death which is the death of your flesh. Those who heard the voice of God ( the gospel ) preached by God's servants and believed everything they heard learn about life after the death of the flesh. Those who heard all about Eternal Life lose their flesh but know that isn't the end of them. They learn that in the New Heaven and Earth, they will get new flesh;
Ezekiel 371: The hand of the LORD was upon me, and he brought me out by the Spirit of the LORD, and set me down in the midst of the valley; it was full of bones.
2: And he led me round among them; and behold, there were very many upon the valley; and lo, they were very dry.
3: And he said to me, "Son of man, can these bones live?" And I answered, "O Lord GOD, thou knowest."
4: Again he said to me, "Prophesy to these bones, and say to them, O dry bones, hear the word of the LORD.
5: Thus says the Lord GOD to these bones: Behold, I will cause breath to enter you, and you shall live.
6: And I will lay sinews upon you, and will cause flesh to come upon you, and cover you with skin, and put breath in you, and you shall live; and you shall know that I am the LORD."