Many relationships were broken over business deadlines, pressures and stress, sometimes through burnouts. Generally when there is a case of burnout, it is extremely hard to then preserve the relationship.
The key issue with deadlines is that they are flexible in 99.9% of cases. Good managers understand that. Bad managers would pressure employees and break relationships. As a result, among broken relationships and employee exodus every possible deadline is also missed by a lot.
Extrapolating on the previous idea, this is just something else to always keep in mind. Former employee may become your friend or your customer in the future. Good relationship would help there. Broken relationship can do a great degree of damage.
Supervisee has an important role in any relationship-building. Another way to phrase this is to say that the manager cannot succeed without supervisee doing their fair share. If it does not work, it does not work – and best would be to realize this as early as possible.
While the relationship still exists it is not too late to start working on it. If the employee hasn’t quit yet, even if there were a lot of issues in the past and the relationship is brittle, it is not too late to improve things.