BBL worth it? Will the fat just shrink o go away completely after a couple of years?

There are a lot of variables that affect fat retention after grafting.  The technique of harvest and purification can affect the viability of the fat.  You can purify and concentrate the harvested fat to remove non fat liquid components using a variety of methods.  1200 cc of harvested fat might be 50% tumescent fluid and injecting this results in only 600 cc of actual fat put in (without processing to remove the fluid prior to injection).  Experts still disagree on the necessity of concentrating the fat prior to injection and on the actual method of doing this (filter systems, centrifuges, etc.)
There is a limit to how much can be injected in an area and expect to survive.  This makes depressed areas like hip dips challenging because the exact region you want to inflate the most has the least tissue to inject into.  If you over inject an area, the fat likely does not survive very well if at all.
There is not a lot of consensus regarding garments, length of time to use them, pressure avoidance on the grafted areas, etc.  and to my knowledge there are no studies that specifically look at this.
In my experience (and I generally place 250-500 cc of concentrated fat per side) the survival is about 50-70% in the subcutaneous plane at one year.  It is not uncommon to have to treat the hip dip area a second time.  I think I get good results with more modest grafting combined with precision liposuction of the hip and back as well as sometimes the lateral thigh area to create a nice curve from trunk to legs.  
I have revised the result on patients who went elsewhere for massive fat injections and ended up with suboptimal contour.  I think those seeking high volume fat graft to the buttock really need to do their research and find a board certified PS with substantial experience in this variation of BBL and a solid track record.  Also (and perhaps because I have been around a long time now) I caution those who seek significant exaggeration of their figure at an early age to be mindful that this can have adverse consequences to their appearance with aging.  

Fat is a great filler because it has long lasting results.  After a BBL, some fat will be lost during the first few months but after that it should last long term.  However the size of the buttocks will fluctuate with weight gain and weight loss. However it should not go away completely after a few years.

Modern techniques of fat transfer offer long lasting and excellent result.  For safety, BBL fat should always be placed in the subcutaneous/gluteal fat above the muscle.  Fat should be placed under low pressure and not overfilled which can result necrosis.

My advice would be to find the plastic surgeon with the best credentials who has performed hundreds of BBLs.  I transfer 1200 cc to 1500 cc per buttock after liposuctioning 5 liters.  This inevitably produces outstanding, noticeable results.  Many surgeons do not transfer enough fat, and that is the reason for less than wow results after a year.  I have followed these patients for over a year, and the results last if you follow post-operative protocols.

Dear BrownCowgirl,
in most cases 30-50% of transferred fat will be lost. Fat viability depends a lot of surgeon technique. The fat has to be placed back into the buttocks as soon as possible so that it has a greater chance of survival. It has to be placed carefully so that not too much fat is placed in only one area. If you are considering a surgery, I would suggest you to consult a board-certified plastic surgeon. Only after a thorough examination you will get more information and recommendations.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

Hello dear!!
Thanks for the question and provided information as well. 
After a BBL, only about 70% of the transferred fat cells will survive, so it is normal to see a minor reduction in your buttocks, but without a major weight loss, you should be able to maintain the volume over time.l recommend you to make an appointment with a board certified plastic surgeon to talk about your goals and anything you need to know.
Good luck :)

~30-50% of the fat volume injected survives permanently. You want to be at a healthy stable weight at the time of surgery, so that you can maintain the results. If you gain weight for the surgery, then lose that extra weight post-op...then yes, your butt will shrink away. If you maintain the pre-weight surgery, the 50-70% of the fat volume that survives will be there permanently. I have long term results that look amazing still. When you experience the fat volume loss of 30-50% over the first 6 weeks to 6 months, you feel like you "lost" everything (you get used to it being really big)...BUT then when you see your before/after photos, you will appreciate that you still have a significant difference. 

The results of your BBL should be long lasting as long as you take care of your body. High definition VASER liposuction provides the newest technology. More fat can be harvested and grafted with much more viability, meaning the fat cells have a way better chance of surviving.  A Skype or FaceTime consultation with a BBL specialist can help you get an accurate recommendation and pricing. 
Respectfully, 
Arian Mowlavi MD, FACS
Realself 100 Hall of Fame Inductee

A certain percentage of grafted fat will not survive. Typically results are fairly close to final at about six weeks. By three months patient should not expect to see any further change. Providers will argue to some point regarding what percentage of that survives. Most of this is anecdotal or subjective. Most providers agree that 40 to 60% of that will survive. After three months patient see very little change in the process of fat resorption does not continue for several years.Generally speaking an area of soft tissue can be doubled in thickness during the procedure. Final results are probably somewhere between 50 to 100% increase in soft tissue volume. This means if someone has 1 inch of fat on their gluteal area this can be made into one and a half to possibly 2 inches thick with this procedure. If someone only has 1/2 inch of that in the most they could get is 1 inch.These are general statements and I’m sure there are others who will differ on my description. Over grafting in an attempt to create more impressive results tends to create a higher percentage of fat loss. Therefore it becomes self-defeating to a certain point.There’s no question that this procedure delivers permanent volume Enhancement.Still, there are variables and not everyone is going to have the same type of outcome. The two single variables that matter the most are the skill of the surgeon and the candidacy of the patient. some providers consistently deliver high-quality results and others don’t. Some people are good candidates for this procedure and other people are not good candidates and no matter who does the procedure the results will not be great.Variables that make someone a lesser candidate for a BBL include skin laxity, unfavorable pelvic structure, cellulite or a lack of fat to be harvested.Nobody has to have a BBL. The value of this procedure is in the eye of the beholder. The results vary substantially among providers and based on each individual patients candidacy.I suggest having multiple in person consultations with senior board-certified plastic surgeons who have extensive experience with this procedure. Obviously if you talk to plastic surgeons who don’t perform this procedure on a regular basis you may get a very different opinion in regards to how well it works. In regards to being experienced I would say the ideal provider should be able to show you 50 before and after pictures showing consistent high-quality results.Something to consider that is particular to this procedure is only viewing after pictures taken at least three months after the procedure. Because the results change so drastically over time showing immediate after results is misleading and deceptive and sets a very unreal expectation to what can be achieved. Avoid all providers who show after pictures taken on the operating table or with surgical markings still present on the skin.Early results are not even close to resembling final results which in a sense is your main concern. look for providers who show honest results with pictures taken at least three months after the procedure.Best, Mats Hagstrom MD

For most patients, a BBL, with liposuction around the waist and torso, and fat transfer to the buttocks and pelvic frame, is a very satisfying procedure.  The surgery can significantly reduce the waist while adding volume to the buttocks and pelvis.  Although, some of the fat does resorb in the first few weeks following the surgery, most studies show a long term retention of 60% to 80% of the fat that was injected.  Ask your surgeon to show you pre and post op photos of patients similar to your situation.  Best wishes, Dr. Lepore