Upon inspecting the tombstone, each of them would read something different. Namely, they would see the name of their world and their own name, not that of the others.

R.I.P.
Here lies

Earth

This world, its home universe and all its people ceased to exist when Sasami / Okuyasu / Asriel / Papyrus died to the Calamity.

??? - April 11th, 1019

The Ghost remains silent.