Is prayer performed for someone who disappeared (Gha'ib) valid?

Primary text

Prayer for the disappeared person is valid for one month, as the period during which their existence can be known without complete dissipation is limited to that duration. This ruling applies to the praying over a grave. This is supported by the consideration that for one lost at sea or burned by fire, it might not be permissible to pray over them due to their complete disappearance, unlike the lost or drowned person where remnants might remain for prayer. Prayer is valid over a person who drowned before being washed, similar to the absent person in a distant land, because the washing was prevented by an obstacle, analogous to a living person unable to perform ablution or dry ablution, who is prayed over according to their condition.