Ideally, if Grace was back to 100% of what he was pre injury, it would look like this....
WILL: Joe Schmidt
2. Greer Martini
3. Josh Barajas
MIKE: Jarrett Grace
2. Nyles Morgan
3. Te'Von Coney
SAM: Jaylon Smith
2. James Onwualu
3. Asmar Bilal
I've said it before though, Jaylon Smith should never come off the field. When Schdmit needed a blow Martini wouldn't actually be my next guy in at WILL, it would be Jaylon sliding over and Onwualu in at SAM, where he's a proven player....
Really I think you have a 5-man rotation at LB between Smith, Schmidt, Grace, Morgan and Onwualu... The other 4 guys I listed are in the "next group". You play 5 for 3 positions as much as possible, with Smith and Schmidt as your flexible "swing men".
You also have to factor in the fact that ND won't actually be in this "base" defense a whole lot in some games. Against spread teams ND will play a base "Nickel" defense, and depending on the team they'll play "Big Nickel" or "Little Nickel"... So you'll see a lot of this...
LB: Joe Schmidt
2. Nyles Morgan
LB: Jaylon Smith
2. James Onwualu
BN: Matthias Farley
2. Drue Tranquil
OR
LN: Shaun Crawford
2. Nick Watkins