I think you’re underestimating our ability to save our own asses through technology.
Even if all the soil for growing food goes to crap, we can just engineer food crops that can grow in that soil. Hell, NASA has a research project exploring how to grow crops in moon (Or maybe it was martian) soil. Humans are one of the most adaptable species, because if natural processes are too slow we can just augment it through our technological prowess.