“They do not go down to Hades”
“Blessed are the dead in Christ from now on…they will rest from their labors” Rev. 14:13
“I go to prepare a place for you…” Jn. 14:3
“And God raised us up with Christ and seated us with Him in the heavenly realms in Christ Jesus, in order that in the coming ages He might display the surpassing riches of His grace, demonstrated by His kindness to us in Christ Jesus.” Eph. 2:6-7
“...your life is now hidden with Christ in God.” Col. 3:3
Protestants are often ignorant of the worldview of the pre-Christian Hebrew: there was only one place for the dead, and that was the grave, Sheol, or what the rabbis translated to Greek as “Hades”. No one was punished or rewarded in death -- that would not happen until the Great Judgment, which was also the Resurrection.
We must therefore take very seriously the claims in the Gospels, Epistles, and Revelation that those who believe in Christ would have eternal life; would rise to glory in the resurrection; while those who didn’t would rise to judgment in the Resurrection. This was not merely a soteriological promise, but an eschatological one, which, by the end of the Gospel narrative, became not a promise, but an accomplished fact.
I will restate a foundational principle: if Christians go to heaven when they die, then the Resurrection and the Great Judgment is fulfilled. This is the full preterist position.
I believe that a number of the so-called Gnostic texts were not in fact Gnostic, but spiritual teachings that had as their foundation a fulfilled eschatology. Among them is the Gospel of Truth. We find a very clear spiritual teaching on the fate of those who die in Christ -- that they do not go to Hades, but to God, something which was impossible before the Judgment and the Resurrection.
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Excerpt from The Gospel of Truth:
Each one will speak concerning the place from which they have come forth, and to the region from which they received their essential being they will hasten to return once again and receive from that place, the place where they stood before, and they will taste of that place, be nourished, and grow. And their own place of rest is their fullness.  All the emanations from the father, therefore, are fullnesses, and all his emanations have their roots in the one who caused them all to grow from himself. He assigned their destinies. They, then, became manifest individually that they might be perfected in their own thought, for that place to which they extend their thought is their root, which lifts them upward through all heights to the father. They reach his head, which is rest for them, and they remain there near to it as though to say that they have touched his face by means of embraces. But they do not make this plain. For neither have they exalted themselves nor have they diminished the glory of the father, nor have they thought of him as small, nor bitter, nor angry, but as absolutely good, unperturbed, sweet, knowing all the spaces before they came into existence and having no need of instruction. 
Such are they who possess from above something of this immeasurable greatness, as they strain toward that unique and perfect One who exists there for them.  And they do not go down to Hades.  They have neither envy nor moaning, nor is death in them. But they rest in him who rests, without wearying themselves or becoming confused about truth. But they, indeed, are the truth, and the father is in them, and they are in the father, since they are perfect, inseparable from him who is truly good. They lack nothing in any way, but they are given rest and are refreshed by the spirit. And they listen to their root; they are busy with concerns in which one will find his root, and one will suffer no loss to his soul.
Such is the place of the blessed; this is their place. As for the others, then, may they know, in their place, that it does not suit me, after having been in the place of rest, to say anything more.  It is there I shall dwell in order to devote myself, at all times, to the father of all and the true friends,  those upon whom the love of the father is lavished, and in whose midst nothing of him is lacking. It is they who manifest themselves truly, since they are in that true and eternal life and speak of the perfect light filled with the seed of the father, which is in his heart and in the fullness, while his spirit rejoices in it and glorifies him in whom it was, because the father is good. And his children are perfect and worthy of his name, because he is the father. Children of this kind are those whom he loves.