What should we do with our mosque in an area we are leaving, which will be handed over to non-Muslims; should we demolish it, or leave it, fearing it might be misused?

It is permissible to sell an endowment (waqf) if its benefits have ceased and it is no longer possible to utilize it, whether it is a mosque or something else, such as a mosque whose congregants have moved away. Its price should then be used to build another mosque. This view has been held by Imam Ahmad, Ibn Qudamah, and Sheikh Ibn Baz, may Allah have mercy on them. If it is possible to sell the mosque to someone who will use it for a permissible purpose, then it is permissible to sell it as is after altering its structure. Otherwise, it should be demolished, and its land and rubble sold, with the proceeds spent on another mosque.