It Can Be Permanent
BBL success is highly dependent on surgical technique during fat extraction, processing, and reinjection.
It is also important for the patient to follow the post-op restrictions to ensure success.
When done correctly, fat grafts are permanent. When done incorrectly, they may not last and you may need a re-do. (http://www.cosmeticsurg.net/blog/2009/12/03/recipe-for-permanent-fat-injections/)