One of the many problems with SocSec. If they are unmarried and he dies, she gets nothing and his SocSec he paid in goes to the government. If they get married, she would get the greater of her own SocSec or his. The 'death benefit' is negligible. At least married it doesn't all go to the government.
It's not like he or his adult kids would get anything after he dies.
If my wife goes first, I'm going to marry the youngest legal one that will have me. She can keep drawing the SocSec I earned. I'd rather she gets it than the government.