Don't reproduce at all if the alternative is to give birth to a mixed race in a white country that might make the same eternal argument. If everyone used the excuse of "yes, but if I don't have a child with the different race, maybe I won't even be able to have a child with someone else," the result with regard to original racial loss would be the same as if you didn't even think of that excuse
If you're looking for us to justify your desire to mate with a foreigner. Don't do it, it is an abhorrence unto the Gods and harmful to both of your children, souls and bloodlines. There are plenty of people compatible with you in the world.