It's not about it being impossible to cryptographically prove/validate it, but rather about services choosing to not attempt to try to validate it. They generally don't provide such an option, because it's tricky, somewhat manual, has certain costs and risks, and no benefit to the service provider.

If some law prescribes that after following a certain verification process, the operator is required to delete the account, then that legally mandated process would work, but in the absence of such a law literally no process can be sufficient, because the operators can and will choose to ignore it, no matter how reliable it is.

If I prepare for it, sure. At that point, I can just leave my password though. I was responding to the point that you don’t need to leave the password because a death certificate would be enough.