Imagine for a moment mankind have become infertile, They try everything from fertility treatments to cloning technology, everything fails.
They haven´t met any other intelligent race in this vast universe, from their standpoint their extinction is the extinction of sentience in the universe .
Suddenly this antinatalist young woman, let's call her Eva, has the last viable egg cells, the goverment persuades her to cooperate and she for some reason agrees. They harvest her eggs for in vitro fertilization using the last viable sperm from the sperm banks, the in vitro fertilization is a complete success but every single attempt to implant the embryos on other women fails.
For some reason she is both the last fertile person and has the last viable uterus in the whole human race. So once again they try to convince her to lend her uterus for the sake of mankind, this time she refuses, they persecute her, threaten her so she hides, some person betrays her, kidnaps her, leaves her in a coma, this person is celebrated as a hero.
They implant an embryo on her,she gets pregnant, the pregnancy is a success, for the first time in a whole generation a new human being is born, a girl who is named Hope.
They saved the human race, humanity died.