I’m surprised that there is no charity who makes it their purpose to document the lives of such people, so that they will have a biographical obituary.
The purpose of the obituary would be so that others could see the connections with them that could have been, to find the still living people who at least knew of them.
I had never considered this but, perhaps, this is a service to which you are being called.
Several years ago, I learned that a retired, former co-worker, had passed away. The news of her sudden death was learned through a quirky circumstance such as you posed. Aside from her employment, she devoted many years to volunteer work - with a local arts council, with Jack Russell Rescue and at a local, historic cemetery, where she added names to the burial register. It was another cemetery volunteer who, while filling in for her one day, began to enter the next name on the list, only to discover that it was our mutual friend! There had been no obituary in the local paper. It seems her family, who had moved out of state years ago, presumed no one would be interested in this woman's death.
Word spread quickly throughout the various volunteer organizations and a service was organized at the woman's Methodist Church. They sent an invitation to the woman's family who were stunned at the SRO turnout for the memorial service.
A similar event took place in my own family. While researching family ancestry, I came across the name of a distant cousin. Curious as to when he had died, I googled his obituary. To my amazement, I learned he had died only 2 months prior. Hopeful that he might have left some precious family photographs behind, I contacted the funeral home. They were equally surprised as my cousin believed he was the last living relative in the family. Several days later, two boxes arrived with all of his photographs. Sifting through them I came across the two photographs I had been seeking for 50 years - my great, great grandparents! A note inside the box indicated that the photographs were scheduled to be shredded that week.