Your organization needs to make sure that they've documented key roles on a deal.
You can use Rollup Helper to assist in validation of the presence of this information.
- Create a text area target field on Opportunity Called Contact Roles Assigned.
- Do a text rollup (concatenation) from contact role name to the opportunity to get the list of all the roles currently identify.
- Build a validation rule that checks if the rolled up text area contains a specific role(s).
- Since this is tied to data validation, should have real-time enabled.