Having species that evolved from us doesn't mean humans don't go exist. There are lots of species we evolved from that have gone extinct. There are only four possible outcomes for the human species. It is possible for more than one of these to exist at the same time:
- We have non-human biological descendents that are a different species from us, and humans are extinct.
- We have non-human technological descendents, and humans are extinct.
- Humans go extinct without any descendants, biological or technological.
- Humans are somehow reproduced in a way that prevents mutation and speciation, such as perfect cloning done by a supercomputer.
Ignoring Option #4, which seems like a means without an end, humans will go extinct long before the heat death of the universe.