I am a psychotherapist and have helped many clients with depression rise out of that dark canyon, never to return. It can take a year or two, sometimes longer, but deep psychotherapy with an attuned, empathic therapist can be transformative. One client said, “At the beginning of therapy I thought I would just have to live with this and you’d just give me a few coping strategies for life. Instead, I gained a sense of self, and an ability to feel joy.”
I believe this is possible in many, many cases.