The winner of the SEC, ACC, Big 10, and Big 12 - get the first four spots, and a bye, in ranked order. Then the next 5 - 12 get spots based on their rankings. The best "Group of 5" team gets in based on their ranking. If lower than 12 - they will be the 12 seed. Notre Dame can be no better than 5th, even if ranked #1.
The best senario for ND. They finish 5th or better. Get the 5 spot. Play the "Group of 5 team" at home (Should win easily). Hopefully, there had been an upset in one of the Power 4 championship games and ND would get that lessor champion in round 2 (Easiest round 2 opponent). Putting them in the final 4.