Anon, understand God works far above physical things like blood types and skin color. That's not to say He can't work at that level too, but God works mainly with your heart, mind, and soul. Besides, even if there was some kind of way to destroy a bloodline, God would simply raise up someone else to teach His word.

No one can beat God, His word is here forever. And yes those against Him will fight it and try to destroy His people. But that's like ants trying to make a sinkhole to swallow a whole nation.