What are the consequences of not healing a midfoot fracture?

Depends. There are several types of midfoot fractures. Some can not heal and may not cause many symptoms. Others may cause severe disability. If you have a non healed midfoot fracture, seek advice from an orthopedic surgeon trained in foot and ankle.
Pain. It depends on the fracture. Non-unions typically cause pain. In the midfoot this could also lead to arthritis and arch collapse.