Hitters usually have a fairly linear development path. Pitchers may invent a new pitch or adjust their mechanics and in the process transform themselves from year to year, but hitters progress more steadily, evolving by steady degrees. Once a hitter has established himself as a regular in the major leagues, it is unusual to see him suddenly regress to the point that, after a period of years and/or a substantial number of games, he has to be sent back to the minor leagues for re-education.
J.J. Hardy and Chris Young were recently demoted to the minors. As previous examples such as Rickie Weeks, Melky Cabrera and Jeff Francouer show, this may help a little, but it likely won't solve the underlying problems.