Many thing. The answer to your question depends on what sort of facial reconstruction you're speaking of. The goal of reconstructive surgery is to restore the normal form and function of the face and facial structures. This can range from removal of a small cancer with reconstruction of a small defect to a face transplant. In general though successful reconstruction can be a transformative experience for patient.
Depends. Many can fully recover and lead normal lives. The results depend on the extent of injury, the level of functional impairment, and the cause of the problem. See a facial plastic surgeon for an opinion.