Using the word soul leads easy to misundestandings. if soul is indeed part of absolut and eternal, there is no way it can be fragmented, as I understand soul. Only ego can be hurt in human being, which is the major tool through our personality operates. And when personality gets hurt, it may be fragmented.
If you reach through meditation into mindstate, where you start vaninshing your sense of indivuality and dualism, merging with whole there is not much left, which can be hurt anyway at all. Everything appear only action of world, which is neither bad or good.
Other's have done good explanations about soul retrieval as a method. I would just use rather word "essence" than soul, which is brough more whole during process. How much does it matter, what way method is called. Maybe it is not so relevant at all. What is, if it works or not. It does not matter much, what people do, if they get wished results.
One thing I do not like at all, is this idea doing of soul retrieval, whithout fully inspecting the situation. It may be wrong way nevertheless. It sounds just so absurd thinking that a person comes to shaman saying: "I need soul retrieval." It is shaman's work to find out what it is needed to do through spiritwork. It may be extraction work or any other way of bringing somethin in or extracting something out.
Soul retrieval or any orher method should not be like taking a universal pill for all problems. Every sitation in unique and should be workd such.