Crisis On Infinite Earths, Part 1: What Does The Ending Really Mean?
3. Argo City Is Lost
24 hours before the wave of antimatter made its way towards Earth, it passed Argo City and, in the process, wiped the last remaining shreds of Krypton from existence. Not only was the whole scene eerily reminiscent of the destruction of Krypton itself, it took the entire population of Argo with it - including Kara's mother Alura Zor-El.
Not only is Alura's death incredibly disappointing, this is technically the second time she has died - following her initial death in the Season 3 finale at the hands of Reign which was subsequently undone by a little time travel - and third time she has been presumed dead (the first of which was after Krypton's destruction).
Superman and Lois would also have been wiped out had Harbinger not transported them out of there just in time.