Depending on the person and how severe their brain injury is, depends on whether they will heal fully or not. Some people may recover completely, but many do not. Even through the best treatment and rehabilitation, the disabilities associated with TBI don;t ordinarily disappear. There are compensations out there that can help with TBI and making long-term disabilities manageable, but they will generally not make the disabilities disappear.
Resource:
Hallahan, D., Kauffman, J., & Pullen, P. (2013). Exceptionality and Special Education. In Exceptional Learners: An Introduction to Special Education (Thirteenth ed., pp. 322). Pearson.