Many things spring to mind with the prompt 'End of the Line'. Do you have an "end of the line" ancestor - one who you're convinced won't go any further back? What about an ancestor who lived at the end of a street, or one who lived in a small town where the train station literally was the end of the line?
For me, the 'End of the Line' is myself, on my father's line at least.
My great grandfather died young, with only one child, a son, to carry on the family name. My grandfather, one of five children, was the only boy to carry the name on to his generation. Although he fathered ten children, 4 of them sons to carry on the family name, the line stops with my generation.
Of the four boys in his family, one was a lifelong bachelor. Two had only daughters. Only one had a son who would carry the family name into my generation, and he had only a daughter. So while my surname is extremely common, the actual paternal line, going back 5 generations, dies out in my generation. While there are cousins in plenty, none of them will carry the paternal surname.
The end of the line indeed.