When a copyright holder dies, their copy rights pass on to their heirs. Depending on the state, this means it can go to cousins or twelfth cousins twice removed if that's all that is alive. Failing that, it goes to the state. Any/all of these could potentially sue if there is money in it.

They could, which is why I said when the copyright holder loses the ability to sue, not when the creator dies.

When it's a twelfth cousin they won't even know they have the copyright. Because it's an implicit right, they don't enumerate all your copyrights and tell your heir about them. The heir has to know.