"Eternity... Humanity... Oblivion!"
The Hulk explores his gentler, childlike side playing with figurines on Doctor Strange's floor. Clea indulges his naivete, when along comes Nighthawk to lower the mood with his tales of woe and self-loathing.
During this dissertation of despair, all existence simply blinks out, not once, but twice. Before anyone can ask, "who turned off the lights?", Stephen Strange is guided in his astral form into the prescence of the cosmos-spanning entity known as Eternity.
Eternity tells Strange of his foregone wishes to fully experience life in all its manifestations. Eternity had created facsimile bodies to live out mortal lifespans. The fragments were all returned to Eternity's whole, except three. Meaning the fabric of reality is incomplete, therefore; all existence may end.
Doc wastes no time in rallying the troops, who each answer the call, except the Silver Surfer; also wallowing in self-pity after another unfortunate episode with the great unwashed masses of humanity.
To cut a long story short, the three fragments had decided that rather than return to never-ending oneness with Eternity, they would rather taste the finality of oblivion. It takes the words of Nighthawk, the least confident of the Defenders to sway the collective conscience of the beings and convince them to rejoin Eternity.