DC’s big summer event for 2015 was Convergence, a nine issue mini series (along with a lot of two-issue companion series) that detailed the heroes of Earth-2 facing off against a newer, bigger version of Brainiac who had harvested cities from not only different worlds in the DCU . . . not only different timelines in the DCU . . . but different universes as well.
Across the companion series, readers were treated to glimpses of the worlds they’d read about over the preceding decades and which had been wiped out by one Crisis or another – characters from the pre-Flashpoint universe were joined by those from pre-Zero Hour, pre-Infinite Crisis and even from the pre-Crisis on Infinite Earths universes.
The heroes in these cities were imprisoned by Brainiac on one world, Telos, for an unknown purpose. When Brainiac attempted to harvest a city from the possible future of the DCU (in The New 52: Futures End series) he was narrowly defeated and imprisoned there. The impact of this was that Brainiac’s servant (and living embodiment of the planet) Telos decided to release the inhabitants and force them to fight each other: this was the rather flimsy reason for the two issue companion series – the fights between the cities were detailed in them.
At the end of the main series, however, Brainiac returns and realises he’s become a monster. Attempting to make amends, he tries to return the various heroes back to their original worlds and timelines, but is prevented from doing so by “the first crisis” – ie, the Crisis on Infinite Earths:
That first Crisis, Brainiac determines, must be altered or the new multiverse will collapse into a single universe once more. Despite saying the outcome must be changed, Flash and Supergirl (who died during it) volunteer to head back and “do it like we did before” which seems to be missing the point. The Parallax version of Hal Jordan, however, steps up and volunteers to go with them:
Along with a handful of others, the heroes are sent by Brainiac to “prevent the collapse of the multiverse” during the first Crisis, thus saving the new version of the multiverse. So they head off, flying back to Crisis on this page:
and then on the very next page, the first caption is:
We have no idea what they did or how they did it or at what point during Crisis on Infinite Earths they did whatever it was they did, but Flash, Supergirl, Parallax, Superman, Lois Lane (along with her and Superman’s son) undid arguably the biggest DC comics event in the time it took you to turn a page, thus saving the current multiverse:
Crisis on Infinite Earths either didn’t happen at all or, at the very least, the events at the end of issue #10 / beginning of issue #11 where the multiverse has become a universe have been prevented or happened differently.
And it all happened off screen.