I say for some it is possible, as I know people who have overcome depression. No, I am not going to blow smoke up your ass and tell you everyone can get better. One must understand this is a very complex topic. We are so different from each other, on so many levels. You have biology, diet, environmental influences, life experiences, life goals, personal loss, and so on. The possible reasons why someone is depressed is too numerous to list. Depression also comes in varying degrees of severity and we each handle these varying levels in different ways. When it comes to depression, we can relate to each other's pain but we have to realize we are at the same time completely different in our pain.
I would say, whatever is in that book, give it a try. Try whatever you can in attempts to improve your life. What might work for one person has no guarantee to work for another so you have to try whatever technique yourself. All I know is that not trying almost always guarantee a non-improving result. I realize that a lot of us, me included, lack the motivation and energy to try and I realize that there is a lot of fear in getting ones hope up and then "failing". There is no shame in "failing" because you get to say you tried. It takes a lot of strength to try and not all of us have that strength. I admit I am in the stubborn category, when it comes to improving one's situation, but I take ownership of that fact.