How do you handle a (possibly ill-advised) deal sellers made with a key employee that they want you to honor in the pro forma company?

Background: Sellers hired a sales rep several years ago whose relationships that transferred grew the business into an adjacent revenue stream that's grown to 20-30% of revenue.

Sellers laid out a milestone road map to give equity if he hit certain milestones. Then COVID hit. The employee never hit the milestones and isn't ready for ownership. Sellers still want me to lay out some kind of a road map to equity for the guy post transaction.

How would you handle it?