At the end of that story, in #166, he was told by his scientist (Prof. Sturdy) that the side effect of his empowerment was rapid aging. Horrified, he went berserk before being stopped by the Avengers. Then, at the end, Sturdy admitted that he lied-- the aging was temporary and would have reversed itself eventually.  (Thus providing the perfect set-up for my own "What If...?" story that can be found on MV1.)

In AVENGERS ANNUAL #9, Nefaria was seen to be held in some sort of suspended animation in a chamber in Avengers Mansion. The reasons for this were unclear; had his aging simply not yet reversed, such that he needed the life support? Or were the Avengers actively holding him in a suspended state precisely so that his aging would not reverse and his powers and youth return in full force? A very interesting ethical question... (A third option is that Sturdy lied to the Avengers when he told them that Nefaria would recover. But this seems highly unlikely. Sturdy had no logical reason to lie to the Avengers and tell Nefaria the truth-- quite the opposite, in fact.)

In IRON MAN #116, we saw a now very aged Nefaria in a wheelchair. I forget if Whitney Frost (his daughter) broke him out of the Mansion, or obtained custody of him legally. He still hadn't, as far as we could tell by looking at him, regained his youth or his powers at this point. During a battle, Iron Man inadvertently shoved the Jupiter landing vehicle onto the machinery supposedly keeping Nefaria alive, and Whitney announced that he was dead.

It's important to note here that the machinery was crushed, not Nefaria himself. If, as Sturdy said, Nefaria had the potential to regain his youth and his powers, it is entirely conceivable that he could survive the destruction of his life support machinery-- he could have easily been further along in his recovery than even Whitney guessed.

Because of this, I've argued for twenty years that Nefaria was not dead; that he could easily return. Thus my happiness at seeing AVENGERS #32-34. Thanks, Kurt.