Presumption of death--Any person missing from his usual place of residence and whose address is unknown by his family or those who, in the ordinary course of events, would be expected to know his whereabouts, who is continuously absent and unheard of for a period of seven (7) years or longer, shall be presumed to be dead and the district court, after the expiration of such period, shall have jurisdiction and authority to declare such person to be legally dead and to issue letters testamentary or letters of administration upon the estates of such persons.