The honest way to underwrite this is in departures prevented. Set the assumption yourself: put a loaded replacement cost on each critical role - recruiter fees, weeks of vacancy, 3-6 months of ramp, and the schedule damage on every active project that person was holding together - then count how many of last year's departures you would have paid real money to prevent. If the system helps you keep even a few of those people, it covers itself; every retention after that is margin. The mechanism is continuity: superintendents who stay keep critical-path activities moving, estimators who stay get sharper against your actual cost history instead of resetting with every new hire, and crews that stay together hold the safety protocols that keep TRIR and insurance premiums down.
The return compounds because retention is cumulative. In the early months, interventions land on the highest-risk critical roles. As the model retrains on your actual outcomes, it learns which interventions your firm's culture responds to - schedule relief, bonus timing, role rotation - and stops recommending the ones that don't work. By the end of the first year you are managing retention as an operational discipline backed by your own data, not reacting to resignation letters.