Or are we talking about how the situation can get so bad by already assuming that the situation has gotten so bad? Assume that there is complete collapse of all civilisation and humans are barely surviving, etc?

Several attempts have been made to explain why Lystrosaurus survived the Permian-Triassic extinction event, the "mother of all mass extinctions",[17] and why it dominated Early Triassic fauna to such an unprecedented extent:

One of the more recent theories is that the Permian-Triassic extinction event reduced the atmosphere's oxygen content and increased its carbon dioxide content, so that many terrestrial species died out because they found breathing too difficult.[14] It has therefore been suggested that Lystrosaurus survived and became dominant because its burrowing life-style made it able to cope with an atmosphere of "stale air", and that specific features of its anatomy were part of this adaptation: a barrel chest that accommodated large lungs, short internal nostrils that facilitated rapid breathing, and high neural spines (projections on the dorsal side of the vertebrae) that gave greater leverage to the muscles that expanded and contracted its chest. However, there are weaknesses in all these points: the chest of Lystrosaurus was not significantly larger in proportion to its size than in other dicynodonts that became extinct; although Triassic dicynodonts appear to have had longer neural spines than their Permian counterparts, this feature may be related to posture, locomotion or even body size rather than respiratory efficiency; L. murrayi and L. declivis are much more abundant than other Early Triassic burrowers such as Procolophon or Thrinaxodon.[8]

The suggestion that Lystrosaurus was helped to survive and dominate by being semi-aquatic has a similar weakness: although amphibians become more abundant in the Karoo's Triassic sediments, they were much less numerous than L. murrayi and L. declivis.

The most specialized and the largest animals are at higher risk in mass extinctions; this may explain why the unspecialized L. curvatus survived while the larger and more specialized L. maccaigi perished along with all the other large Permian herbivores and carnivores.[8] Although Lystrosaurus generally looks adapted to feed on plants similar to Dicroidium, which dominated the Early Triassic, the larger size of L. maccaigi may have forced it to rely on the larger members of the Glossopteris flora, which did not survive the end-Permian extinction.

Only the 1.5 metres (4.9 ft)-long therocephalian Moschorhinus and the large archosauriform Proterosuchus appear large enough to have preyed on the Triassic Lystrosaurus species, and this shortage of predators may have been responsible for a Lystrosaurus population boom in the Early Triassic.

Perhaps the survival of Lystrosaurus was simply a matter of luck.

During this period there was a spike called the Paleocene-Eocene Thermal Maximum event, where CO2 injection rates were comparable to now.