Short Answer

Once a couple is married, termination of that marriage can only occur through divorce [ṭalāq] from the man, the wife demanding release [khulʿ], or through an annulment of an Islamic court/tribunal [faskh]. Therefore, even if the husband and wife lived apart for several years, there would be no automatic termination of the marriage.

Advice
People have a mistaken notion that a long separation results in automatic divorce. This is very dangerous because one spouse might remarry assuming they are no longer married, though they are. The best way for a woman is to contact the husband and have him pronounce divorce, if he is reachable and willing, and her waiting period [iddah] will begin from that point on.

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Shaykh Mustafa Umar