This is being talked about now on the WS game on TV. Evidently Cooper had knee surgery after working the Yanks/Twins ALDS. He was recuperating at his father’s home and had a blood clot, which was the cause.
Probably the biggest compliment one can give a long-time umpire is not knowing he existed. Cooper must have done his job well and stayed in the background – as it should be. RIP.