When a person has been missing for a long time, it is natural for people to begin wondering whether they have passed away. Yet, in Islamic law, Salatul Janazah can only be performed if there is certainty.
Therefore, as long as the death of the missing person has not been established, Janazah prayer cannot be performed for them. Also, Janazah is not ordinarily legislated long after a person’s death.
This is undoubtedly a deeply painful and distressing situation, made worse because there is no closure.