My kindergarten friend's son donated a kidney to his son (the kindergarten friend's grandson.). It was not a great match and the son had a redo a couple of years ago. Last fall the son who donated, who was a cop, was murdered. There was a 20-hour surgery for harvesting all of his organs and tissue. It was the first time that the transplant facility had a donor who had previously donated.
The only down side that I know of was that he, the donor, had left a big busy PD to go to a small one. He was bored to tears, and the big agency would not take him back with only one kidney. He found another department, thrived and their love for him was made evident when they lost him.