When you lose a significant amount of fat do the fat cells die or do they just shrink? if you regain the fat they go back to original size? and lipo?

They generally: Shrink. Yes, they go back to original size. Liposuction can surgically contour areas where there is excessive fat tissue. It is not for weight loss.

Fat cell size: Your fat cells are yours forever. They shrink with weight loss and will become larger with weight gain. A few studies have suggested that conjugated linoleic acid may cause strictly abdominal fat cells to shrink to some extent on a more permanent basis. Liposuction is for body contouring, not weight loss.