You can use the core Salesmachine Metrics to define your Health score.
License Utilization (e.g. % of active users within account) / % of healthy contacts within account)
License Utilization (% of active users within the account) is really relevant for per-seats business models. You can then make sure that your client will not down-sell.
% of healthy contacts within the account is powerful as it allows you to see the level of engagement within an Account.
➕ Upside: great to have a global vision of Contacts' health at Account-Level.
➖ Downside: It can be sometimes biased as some Accounts might renew even if some Seats or licenses remain unused. These Accounts might down-sell though.
This Score is similar to an « engagement » health score.