I wouldn't worry too much. Just cut it clean and another vertical growth should appear in spring. Maples often times don't have one srtrong leader. They usually develop multiple leaders at some point so your original leader would probably not last forever anyway.

kjskjs is right on :-) This is not a concern.......maples and many other shade trees are considered decurrent growers or those that do not develop a true leader. Generally these types of trees will have significant lateral branching that grows as fast as any early leaders do. The point is to develop a well-rounded crown.