Is it permissible to seek divorce from a husband who has been absent for nine years, whose whereabouts and family are unknown, after the marriage was initially intended for a later divorce, and the husband did not fulfill his promise?

Marriage has specific conditions. If these conditions are met, it is a valid marriage, and its validity is not affected by it being for a specific purpose. If this person does not divorce you, you are still under his marital authority, and you can refer your case to the competent authorities, such as Islamic centers, to consider the matter.