In South Carolina the relevant law is §62-3-914, which governs unclaimed assets. First, 8 months after the PR is appointed, the court must be convinced that the party can't be found. Then there is a hearing where interested parties can object to distributing that portion of the estate. Notice of this hearing has to be published three weeks in a row, at least a month in advance, in a newspaper in that county and at the discretion of the court one other newspaper (there are also filing requirements w.r.t. copies of the paper). The crucial next step is
(d) At the time fixed in the notice for cause to be shown, due proof
of publication having been made and filed as required by subsection
(c), if no person appears as required, the court must decree
distribution of the estate to be made as if the person whose
whereabouts or the fact of whose death is unknown had died before the
decedent. Distribution by the personal representative is a full and
complete discharge to the personal representative.
If it is determined that the missing person died after the deceased did, that share is then distributed is whatever way the missing person's estate is to be distributed.