How can a man marry a woman on a remote island where there is no one else besides them, and they cannot leave it, if he wishes to marry her?

What the questioner mentioned is a hypothetical matter that is difficult to occur due to the development of communication and monitoring tools, and the diversity of transportation and exploration means. The predecessors, when asked about such matters, would say: "Leave it until it happens." Indeed, Malik refrained from answering such questions, from which the questioner gains no benefit in their religion.