It's called the 3 percent rule. Nature abhors absolutes. Even if 97 percent of a population is affected by some environmental condition sufficient to cause death at least 3 percent will be resistant to that exact condition and will propagate to form a replacement population. Thus even decendants of Dinosauers still walk the earth today.
The sun could go nova tomorrow and enough terrestrial life has already escaped from Earth to eventually seed a new planet somewhere far, far away from this solar system. It would not necessarily be recognizable to the current population of Earth but it would be from and of the Earth. This would, of course, include some form of the blonde gene.
Hope this helps.
Best regards,