Long time ago (early 90's) I read a Fantastic Four story where the crew was on an expedition inside a parallel Universe. The Universe was destroyed (if I remember correctly, by someone/something triggering the Ultimate Nullifier) and although FF got out just in the nick of time, Johnny's girlfriend died with the Universe.
What story was this?
It has to be Fantastic Four issue 341 from June 1990.
While the FF is trying to stop a future Galactus from destroying the universe a woman called Nebula (not the one connected to Thanos) possesses Sue and activates the ultimate nullifier.
As the team races to escape the blast radius on the timesled (Rosebud II) Johnny reaches out to save Nebula but she is caught in the blast.
The comic ends with the team ending up in another alternate universe where Stalin is still alive and America and Russia is about to go to war.
I believe that was the Infinity War.
At the same time, on Earth, legions of super heroes were being attacked by twisted clones, or doppelgangers, of themselves. Unbeknownced to the general super hero populace, the clones which managed to subdue their real versions took the place of their doubles and continued along, pretending to be unaffected.
Eventually, it was discovered that the cause of everything was actually the Magus, the purged, evil side of Adam Warlock. Despite being believed dead, the Magus returned in order to collect the Infinity Gems to make the Infinity Gauntlet and reverse the decision made by the Living Tribunal that they would never be used together again.
