Humans have been around for at least tens of thousands of years. And there is a good chance we will survive for a while longer. But how long? There are several reasons that point in the direction of human extinction—an event where humans, as a species, cease to exist. They include the fact that nearly almost every species to evolve has gone extinct, the fact that humans have developed the technological means for extinction (e.g. bioweapons, nuclear weapons), and the great filter.
Such reasons are hardly conclusive, but they strongly suggest that there is a very good chance that humans, at some point, will go extinct—it would be strange to expect that our species would survive indefinitely given the age and lifespan of the Earth and the Sun. So, it is a plausible assumption that humans will go extinct in future, though predicting when is a fool’s errand because it is too easy to wrong about such specifics in the future.
You might be asking: so what? This plausible assumption looks like it conflicts with theism—the view that there exists an all-powerful, all-knowing, just and loving creator of the universe with the title ‘God’. The plausible assumption that humans are bound to go extinct, long before the heat death of the Sun, is in tension with theism: if God created humans in order to have relationships with those humans, God wouldn’t allow humans to go extinct—that would be antithetical to the aim of creation. Here one could point out that humans didn’t exist for the overwhelming history of the universe as we are but latecomers to the evolutionary scene. To which I respond: that’s another problem for theism—one would expect the universe to be better designed if the aim of creating the universe is to allow for the evolution of sentient, moral agents with which God could have a relationship. Unfortunately, the universe appears poorly designed for that purpose.
So, then, we should conclude the real possibility of human extinction, in the future, is some evidence against theism. Here, though, the theist could respond by appealing to skeptical theism: the view that our knowledge of goods and evils fails to exhaust the actual universe of goods and evils. Such vastly incomplete knowledge of actual goods and evils undercuts our epistemic ability to make broad, sweeping claims about what God would or wouldn’t do in a given situation, up to and including human extinction. Perhaps this is plausible, or perhaps the real prospect of human extinction should weaken one’s commitment to theism. You decide.
Yeah but two of the dominant strains of monotheism hold (alternatively) that:
1. Humans won't go extinct, or at least not permanently. They'll be resurrected on judgement day and live forever thereafter.
2. Humans won't go extinct in the relevant sense. Their bodies might, but they will live on (and have a relationship with God) forever in a spiritual form.
I don't see how your argument gets going against the theist without begging a large part of the question against the central tenets of their religion.