if you can't lick them, join them
If you cannot defeat an opponent or get him to change his attitude, plans, or ways of doing things, the best thing to do is to change your ideas, plans, etc.
"The small car manufacturers are winning over the big car makers," the president of an American car factory said. "If we want to stay in business, we must do as they do. In other words, if you can't lick them, join them."