Mo. Rev. Stat. § 473.707

If, within such period of twelve weeks, evidence shall not be offered satisfactory to the court that said supposed decedent is in fact still living, then it shall be the duty of the court to issue letters of administration to the party entitled thereto; and said letters, until revoked, and all acts done in pursuance thereof and in reliance thereupon, shall be as valid as if the supposed decedent were in fact dead.