What should I do if a fat necrosis lump has lasted over 2 years?

Areas of fat necrosis can be treated surgically;  nonsurgical management is an option also. If the area of fat necrosis is small, it may take a few weeks or months to dissipate;  for larger areas, it may take several months (or longer).  Sometimes, patients will experience drainage as the unhealthy tissue liquefies and makes its way out.    In cases, like yours, where the fat necrosis remains longer-term, patients need to consider the pros/cons associated with excision.  Overall, if the area can be excised, without causing significant "deformity" or breast asymmetry, I would recommend excision (so as to avoid interference with self breast exam and/or breast imaging).

 Best wishes.

Hi and welcome to our forum!
A breast mass following breast reduction most likely represents fat necrosis, but could also represent a mass of different cause, unmasked by removal of excess tissue. As it has been getting smaller over time, it suggests the former. After 2 1/2 years, the lump most likely has settled down to its final size. 
If radiographically benign and not demonstrating change, it can be left alone, although some may desire removal. 
Speak with your plastic surgeon regarding pros and cons.
Best wishes...

Fat necrosis can occur following fat transplantation. This will result in the fat cells becoming calcified or hardened which you feel as a lump. These fat cells will be gradually reabsorbed by your body. You can help this process by messaging the caclified cells thereby breaking them down into smaller pieces. This process does take a few years to be completed. If you have tenderness or it the lump is large, you can have it removed by excision.