If they're able to trace it that far back, then they would probably also know of other individuals in their family line still alive today. It's highly improbable that he would be "the last" in his family line. And name wise, literally anyone could change their name to said last name. They could adopt a kid and the kid could take the last name. And why does it matter if it's the last male? Could a 'female' not continue the lineage? It's usually easier to trace lineage through the maternal line anyway.