First, the species of amphibians that existed 250 million years ago no longer exist today anyway.
Second, the article does say that humans are probably responsible for diminished numbers of amphibians, but it also says the nail in the coffin is suspected to simply be natural disease (fungus).
Third, if all of humanity dies, it won't be a 'better' place because nothing alive besides humans can appreciate 'better' abstractly. Perhaps there will be more room for other species of animals, but I don't see how having more animals in general is somehow a great ideal.
Anyway, the reason we care at all about something like amphibians dying is because if our ecosystem collapses we may die as well.
Frogs don't care.