It is narrated from Sa'id bin al-Musayyib that Sayyiduna Umar bin Khattab, may Allah be pleased with him, said: If a woman's husband goes missing and it is not known where he is, then from the day his news is cut off, the woman should wait for four years. After four years, she should observe the waiting period ('iddah) of four months and ten days, and if she wishes, she may marry another man.

Imam Malik, may Allah have mercy on him, said that if a woman's waiting period ('iddah) has passed and she has married another man, then the first husband no longer has any right over her, whether the second husband has consummated the marriage with her or not.

This is also the ruling according to us.
Imam Malik said that if the first husband returns during the woman's waiting period ('iddah), then he will have the right to his wife.

And I found people rejecting the statement of the person who says that if she marries another man, and then the first husband returns, then according to Sayyiduna Umar (may Allah be pleased with him), the first husband has the option to either take his dowry from the second husband or take back his wife.

Imam Malik, may Allah have mercy on him, said: It has reached me from Sayyiduna Umar, may Allah be pleased with him, that he said: If a woman's husband travels to another country and sends her a divorce from there, then takes her back (revokes the divorce), but the woman does not know of the revocation and she marries another man, then if the first husband returns, he will have no authority over her, whether the second husband has consummated the marriage or not.

Imam Malik, may Allah have mercy on him, said that I like this narration and the narration of the missing person very much.