We're pretty good at science
I know, I know- scientists probably declared the Earth flat and immediately said: “We are the BEST at science”. Many scientists were and continue to be idiots, so boasting genuine progress seems hubristic.
But science operates differently these days. We are vastly more capable of identifying the variables in experiments. We've created synthetic cells. We understand how your tiny mono-cellular existence metabolizes and expands into sentient trillion-celled life. These discoveries generate new techniques, and one of these is the de-extinction of animals.
"You can't clone from stone"
My mind conjures woolly mammoths lumbering around the icecaps or sabretooth tigers stalking Pomeranians in the suburbs, but this isn’t likely.We would need new-ish, intact DNA for those animals. So far, all we've done is the Pyrenean Ibex. It was hunted to extinction, only to be resurrected 10 years later- not exactly pre-historic.
Imagine the potential for other organisms, though: new plant compounds, for new drug therapies. New fruits and veggies. A new insect when our agro-assault on nature succeeds in trashing pollination systems. Replacement critters, to fill the void left by the Pomeranians. God knows what we could drudge up. Although it's fun to think about reproducing Velociraptors (ie: to hunt down the Cartel) or Brontosaurii (ie: for burgers), there are more beneficial applications of these efforts.
TLDR:99% of the species that have existed on Earth are gone, but maybe not for much longer.