For nearly all of us, a gravestone or other physical memorial is in any real sense as temporal, as evanescent, a thing as we ourselves are. For when such memorials no longer serve as a token, reminder, or feeble proxy for the deceased in the minds of those who knew them, they simply display a name — and a name, unattached to the memory of an actual person, is just a string of letters.
When the reference to memory is broken, at last, with the death of all who knew him, a person ceases, in any imaginably meaningful sense, to exist. It is a second, and final, death.