Telling someone to cut ties with a demonstrably abusive parent is always good advice.
The problem of Mormon parents demanding respect from their children is age old, and the only way to break this horrible cycle is for the children to stop fulfilling this unwarranted need for respect. Parents believe they lose all their blessings if a child of their's strays from the fold. This narrow-minded belief makes it nigh impossible for the OP's father to start a discussion that doesn't involve the son's eventual return to the cult.
The problem of Mormon parents demanding respect from their children is age old, and the only way to break this horrible cycle is for the children to stop fulfilling this unwarranted need for respect. Parents believe they lose all their blessings if a child of their's strays from the fold. This narrow-minded belief makes it nigh impossible for the OP's father to start a discussion that doesn't involve the son's eventual return to the cult.