What exactly happens to the victorious fat cells from fat grafting? Do they grow/shrink/maintain size?

A
blood supply is necessary for fat cells to survive. Some surgeons overfill and
the fat cells that do not receive a blood supply die. The dead fat is
reabsorbed by the body. The surviving fat cells can grow or shrink or stay
the same. This all depends on you. Did you gain weight? Then your fat cells
will grow or plump up. Have you lost weight? Your fat cells will shrink. If
your weight stays the same, the fat cells should remain the same. This is the
nature of fat cells. In addition, if your cells from your abdomen have been
transferred to your breasts, and your abdomen is normally where you gained
weight first, then now those fat cells in your breasts will continue to behave
the same way as they did in your abdomen, and plump up first when you gain some
weight. 
So,
if you had a fat transfer 6 months ago, and your breasts are small but your
weight hasn't fluctuated, chances are most of the transferred fat
died. This happens often when the blood supply is not nurtured immediately
after surgery. It needs to be stimulated for several weeks after surgery in order
to expect the best results and achieve the highest fat survival rate.

The grafted fat cells which survive will maintain their size and would grow only if you put on more weight. Yes 6 months post fat grafting is the approximate time when you can expect to see the final result.