I think he helped restore some discipline (which was needed). I think he coached up the O-line.... that only really came together in 2020 (note: Grimes was at BYU 3 years). If the other coaches were taking notes on what worked and what did not, they'll be fine. A-Rod has seen coaching of the O-line at uu and BYU. He knows what to look for.
We'll see how things go.
Other recent 'huge' losses: Steward as RB coach, Pugh as OL coach, Kaufusi as DL coach.... and BYU survived.