You may not actually have fat necrosis.
To answer your question, though, fat necrosis typically does get better on its own, one way or another...but if it's persistent it may have turned into scar tissue. At that point it can be revised either with surgical removal, or possibly with some lipo to contour the area.
More likely, though, is that it's not fat necrosis. This entity normally presents with redness and swelling, and fairly quickly proceeds to drainage and an open wound. It usually heals well although possibly with a deformity of some kind that can be modified to a greater or lesser degree.
Instead, you may have some persistent fat, or skin, or scarring from a hematoma or seroma. Finally, it may be intra-abdominal.
You should discuss this with your plastic surgeon and, if appropriate, seek additional consults to get an idea of what you have, and what can reasonably be done about it.
I hope that this helps, and good luck,
Dr. E