Is a woman entitled to seek divorce from her husband who has been missing for a year and a half and suffers from a mental condition?

If a man is absent and his absence outwardly suggests perdition, his wife should observe the iddah (waiting period) of death for four years, and then she may marry. However, if his absence outwardly suggests safety, she should not marry until she ascertains his death or he divorces her. If the wife is harmed by her husband's absence, she may refer her case to the Sharia judge to have her harm removed.