Notre Dame opted out of its contract with Michigan St. that would have seen the two teams play football games in 2014, 2016 and 2017, and nobody was quite sure why when it happened. The two schools have a tradition of playing, and the news came out of nowhere. If what Michigan St. is saying is true though, there hasn't been much discussion between the two schools since the Fighting Irish opted out.
According to the Detroit Free Press, Michigan St. athletic director Mark Hollis said that Notre Dame and MSU have had "no contact" regarding future changes to their series. The current deal requires that Notre Dame and MSU play through 2031, with breaks in 2014-15, 2020-21 and 2026-27.
With the three games already opted out of, there's no word on the rest of them. The prevailing theory is that this is related to Notre Dame joining the ACC. While the Fighting Irish will remain independent, it would mean they play multiple games against the ACC each year, meaning they'll have to eliminate games somewhere.