“there’s been … enough killing …”
Cosmic reboots meant that the far-distant future of the Legion of Super-Heroes was a persistently changing landscape. The loss of the Superman Family from their history – temporarily, anyway – meant that the Legion had to embrace alternatives, such as Kent Shakespeare (codename: Impulse, just a scootch before Bart Allen showed up bearing the same name). With his Superman-like powers, familiar build and glasses, Kent was clearly meant to evoke the idea of the Man of Steel, although he was originally unrelated. A few more reboots fixed that, making him the 31st century inheritor of the Superman Dynasty ... at least for now.
Kent Shakespeare was joined in his incarnation of the Legion by Laurel Gand, codename: Andromeda, who filled in much of the missing backstory formerly involving Supergirl. Her ancestor, the time-tossed Mon-El, served as the Legion’s inspiration, standing in for Superboy.
No one stood in for the Legion of Super-Pets, to the best of my knowledge.