Stockholm Syndrome. The captive defends the captor. Wanting to survive is the cause. Once in its grasp can the captive defender ever come back to normalcy? How?

In the same manner as anyone with any obstacle.  Some do, some don't and some die.

There are psychiatric specialists.   They can, through much counseling and behavior modifications, and a LOT of work and willingness to get better on the part of the client, assist in bringing the afflicted person back to normalcy.