Is iddah obligatory for a woman whose mujahid husband is missing, and is it permissible for her to marry, especially since he permitted her to do so by saying: "If I die, marry"?

The woman remains under the marital bond of her missing husband and is still considered his wife unless proven otherwise. Therefore, she does not observe the waiting period (iddah) of death, nor can she marry another man. If his fate is unknown, his wife is treated according to the ruling concerning the wife of a missing person.