Where Does 'Dead' Fat Go After a Fat Transfer?

Fat injections or fat grafts transfer fat cells from one area of the body to another. Some of these cells die because not enough oxygen can reach the center of the mass of the cells. We try to inject small amounts in one area for this reason. The cells that do not live get processed by the normal human tissue response of the immune system, including macrophages and lymphocytes. The cells get taken to the liver where they are processed. Infection can occur with any filler, but this is a rare occurrence.

Fat cells are mainly made up of lipids and fat molecules.  Dead fat cells essentially break up by your white cells, a process known as phagocytosis.  Some will also be absorbed into your circulation as lipids or fat molecules.  The lipids will then be transferred through your circulation and further broken down, mainly by your liver. 

Fat cells are composed of many molecules but essentially consist primarily of fat in the form of lipids and triglycerides. These are broken down and generally absorbed in to the blood stream and metabolized by the liver and other organs. Studies have been conducted to see if this short term surge is a cause of hypercholesterolemia and it does not appear to be.

In fat transfer some of the fat will not take and the fat cell will die. The content is absorbed by the body and transported via the blood to the liver where they are metabolized. This is true in many surgeries, some fat cells do die, or injured due to surgery they are recycled and removed by the body defences. Some of the contents of fat cells will form "fat cysts" not harmfull.
Infection is caused by bacteria, not dead fat cells. If bacteria is present in enough quantities then infection occur as in any other surgery.

Every living cell requires a certain level of blood supply to stay alive and maintain function. If the blood supply is not sufficient, the cell dies, disintegrates and further broken up by a sub group of our white cells. Their contents ultimatelt end up in the circulation to be used by other cells in our body.

The fat cell is basically a thin walled "balloon" filled with globules of fatty acids or triglycerides. If the transplanted fat cell doesn't take the cell membrane breaks down and  fatty acids are absorbed into the surrounding tissues.These fatty acids are eventually metabolized by the liver the same way that ingested fat would be metabolized.
I prefer to deposit the fat in multiple tunnels especially in the muscle layer where it has a better chance to take.It is important to do the technique properly so as to avoid pooling of fat. If there is too much dead fat in an area it can form cysts and possibly be a source of infection.

You are correct. When we transfer fat to any part of the body, face or buttocks, not all of the fat cells survive. These cells which do not survive will be broken down and their contents (fat-fatty acids and triglycerides) will be absorbed into your blood stream and either taken up by your liver or other cells. There has never been shown to be any harmful effects from this.
As far as getting an infection. You cannot get an infection FROM the dead cells, but there is always the possibility of them getting infected. ie: they will not cause an infection. I have never seen a patient get an infection from fat grafting.