After a facial fat transfer, where does the reabsorbed fat go?

Fat cells that do not survive, atrophy (shrink) and die and get resorbed by surrounding cells. They do not accumulate anywhere else in the body. 

Very good question. Facial fat transfer is the process of taking unwanted fat cells from one area of the body like the abdomen or hips, and then injecting it into areas of the face to smooth away lines, restore youthful volume and provide subtle facial sculpting. Most doctors will inject a bit more fat than you need with the knowledge that some with be reabsorbed. 
When this occurs, the cells are reabsorbed into the bloodstream. They do not migrate to other areas of the face or body. The cells are metabolized and eliminated from the body. The fat that is not reabsorbed can become a permanent facial enhancement. This procedure requires expertise and precision to produce a natural, long-lasting result, so be sure you work with an experienced, board-certified dermatologist to ensure an optimal outcome. 

Facial Fat Transfer is an excellent treatment option for adding volume to the face.  While Dermal Filler is more commonly sought out, Facial Fat Transfer can be a more long-term solution as well as more natural as it requires using donor fat from elsewhere in the patients' body. The fat cells that didn't survive the transfer are then absorbed by the body.

Fat transfer results are permanent, but not all fat will survive. Harvesting is important to fat transfer. Yes, I use water-assisted fat harvesting which gives pure fat to transfer and combine with platelet rich plasma (PRP) to get the most viable and sustainable fat cells. This can be combined with Sculptra, depending on treated area, to improve outcomes. I recommend getting a formal evaluation with an expert. Best, Dr. Emer

Your body will likely recycle this fat - i.e. use it as fuel or if you have adequate calories, will store it as new fat elsewhere.

This is an excellent question, and it is very closely related to another question about fat grafting, which is:  how much of a fat graft survives.  Even though we understand quite a lot about fat grafting already, there is still very much we don't know.  Thus, any answers to these questions will be mostly speculative.  Most of the time you will see percentages anywhere between 50% to 80% for estimates of how much volume in a fat graft will remain over time.  In truth, this is probably related to many variable factors including techniques of the surgeon, amount of fluid present in the injected graft, methods of harvesting, preparing, and injecting fat, and probably factors related to the individual patient too.  As far as what happens to fat grafts, this is also an area of hot discovery right now.  One thing we have recently come to understand is that the adipocytes - the actual fat/oil containing cells in a fat graft - do not survive at all.  None of them.  The things that appear to be responsible for the effects of a fat graft are the differentiation of the immature progenitor cells (let's call them sort of "stem cells" for now) into mature fat cells once they are injected into a new site, and the complex chemical messaging that occurs between the substances and cells in the grafted fat and the local cells already present in the site being grafted.  Thus, it's not just as simple as cells being injected, with some of them dying, and we just see a proportionate increase in volume depending upon how many cells "make the trip."  In some instances, our processing of fat grafts, as in creating nanofat for injection, is intended to actually destroy the mature adipocytes and NOT transfer them.  Any cells, fragments or portions of cells, or cell by-products, like fatty oils, are handled by the body's mechanisms for dealing with dead or dying cells, cellular debris, or other foreign substances.  These things get "ingested" by certain scavenger cells, absored into the bloodstream for transport to organs like the liver or kidneys for detoxification, or walled off and segregated from healthy normal tissues.  Any "accumulation" of any of this would likely stay put right where it was injected and not travel anywhere else in the body.  Again, the degree to which these things happen - or have to happen - is to some degree dependent upon how the procedure is done.

Dead and non-viable tissue is managed through the bodies immune system with white blood cells primarily macrophages absorbing particles of tissue.  Some of the fat also breaks down into oil which is processed by your body mainly through the liver.  I suppose in that sense it adds a certain amount of calories that could be used by your body in other areas.  In reality you can think of the fat is just disappearing  Best, Mats Hagstrom MD