Is it permissible for the one who endowed land for a cemetery to revoke his endowment, or part of it, especially since he owns nothing else besides his private residence?

It is not permissible to revoke a waqf, neither wholly nor partially, because the land has exited the ownership of the endower upon endowment. This is unless there is a need for it in that area for burial. Otherwise, it should be sold and its price used for another cemetery. No action should be taken regarding it except with the knowledge of the judge of that region. The diminished financial state of the endower after retirement does not justify revoking the waqf.