The scarabs can exist because they live underground and all life is only dead on the surface. Same reason as why there still exist flowers and young seed pods underground. Now the seed pods who still haven't run out of water despite how the salamanders haven't sent any of them up for millions of years is more interesting. Presumably they can grow on their own without the salamanders, just like the mushrooms of LoWaS also exist in the wild. But that means that the pod that the salamander cultivated flew away a long time ago and has been replaced by another one at the exact same spot. Which is still within the realm of possibility although it seems somewhat contrived to me.