It will take more than nuclear winters, volcanoes, or asteroids to wipe out life on Earth. Short of a supernova or another event that heats the surface of the earth to hundreds of degrees Centigrade, everything from archaeic bacteria to tardigrades will survive any catastrophic event and eventually more complex life will evolve again. The earth's biosphere will far outlive any civilization.

But we're not talking about tardigrades and bacteria: we're talking about millions upon millions of species that do have complex interdependencies with each other and the environment in general. We have no way to predict which species, when together decimated, might drastically impact our survival because they hunted pests that killed major oxygen producers or transmitted diseases through different animal and human populations. We have no way to know where in the equilibrium we are and which levers might set off a catastrophic downward spiral.

Hell, if there is a nuclear winter or asteroid impact, we are far enough along technologically that many humans, maybe even millions, would survive and rebuild civilization (say using nuclear power, chemical engineering, desalination, and hydroponic agriculture to survive underground until the environment clears up). I guess it just depends on how you define the biosphere and survival.