I love the placerias. Round, slow moving, herbivorous. They must have been a thrill to see so long as one did not enter their safe space. So wonderful to watch not like the killers which would love to tear you appart and eat the pieces.
Dicynodontia would have probably survived for a while longer but might get outcompeted by other megafauna(similar to how stegosaurs got out competed by more efficient fauna)
One major gripe here. You selected the wrong predator. The Prestosuchid Saurosuchus was native to South America and would not have encountered Placerias or Vancleavia. The correct predator would have been either the Rauisuchids Postosuchus or Vivaron the former of which has been confirmed to have frequently preyed on Placerias.