Notre Dame athletics will move from the Big East to the ACC, outside of football and hockey. The Big East requires 27 months notice for departure, but one would imagine that will be negotiated.
The football team will remain independent, but will play five ACC teams per year. How that will affect MSU/Michigan/Purdue is yet to be seen, although this Yahoo story says Notre Dame made the move because of the uncertainty of future scheduling.
ND is playing four current/future ACC teams this year, so it won't be a radical change, but the Irish want to keep games against USC/Stanford/Navy to stretch the brand coast to coast. Will there be enough room for the Big Ten teams? Who knows.
Stop saying Notre Dame is irrelevant.