In order for a missing person to be declared dead the missing person has to be missing for 7 years minimum.
Still even then the person could still be alive and just has gone missing and may not want to be found especially if they're an adult.
I had a friend go missing for a long time and after 7 years it was presumed that the person was dead but then a few years later I found the friend in another state when I went traveling.
It happened to be that the person just left without letting family know about it and didn't want the family knowing where he was.
I told the family that he was safe but he didn't want them to know his exact location which I respected.