Just because some do NOT marry, does NOT mean that there is no offspring. I have run into several so died out lines that in fact there are offspring.
I think that when more people are involved with the DNA research, we will find more.
I also have found DNA changes from one generation to the next, so the family name is not really the blood line name. I have one that was raised as a "Smith" but the blood line is a "Jones". The involved person, did find this out and then legally had his name changed to "Smith".