Nice question. I really like it but the truth is, it's almost impossible for mankind to go extinct. While in the beginning, man's evolutionary path led to a few stages of morphological changes, the major differences between the homo erectus, habilis, sapien, etc is the increase in overall intelligence. Mankind has developed physically over all the years that we've existed but unlike other animals, we've gotten smarter as we've evolved. And that increase in intelligence is what has put us on top of all other animals.
Now for what I said earlier. It's almost impossible for man to go extinct and this is because of our intelligence. Mankind is capable of problem identification and we are very much capable of problem solving. If ever a global problem arose that could make us go extinct, we'd find a solution to the problem. And if by chance it was something that would ravage us totally without us being able to do something about it, then it would probably have the same effect on animals too. Basically I'm saying that anything that will bring about the end of mankind will equally bring about the end of other animals too.
So in essence, unless Thanos personally snaps us away, then we're not going anywhere for a very very very long time
We humans are the most intelligent species among others so I don't think that would be possible.
Extinction is often caused by a change in environmental conditions.
When conditions change, some species possess adaptations that allow them to survive and reproduce, while others do not
Most scientists would agree that humans have greatly affected the process of evolution, from the rise of antibiotic and pesticide resistance to the largely human-caused increase in the extinction rate.
Our effect on the process of evolution even extends to our own species' evolution
You have asked a very interesting question and I love the fact that your question has the word, IF - which is purely conditional.
If evolution is true and considering the fact that it hinges on the fact that species evolve overtime to better fit into their societies, therefore it follows that homo sapiens is the peak in the evolution of mankind.
So, while it is almost impossible for mankind to go extinct, if that happens the new species will be an hybrid human being that will be more capable and intelligent than man. I hold this view because evolution has proven to always be progressive.