I just read about this a few minutes ago, and I'm just really at a loss for words.
We sure have been losing a number of the Muppet family as of late... Jerry Nelson, Jane Henson, now John Henson... this is really sad.
It was interesting reading about John in Jim Henson: The Biography, he seemed like the wildest of the Henson kids, but it was clear that he was really close to his father. Reading about Jim's death in the last chapter was hard enough with all the details of his last days and final hours, but it was just sad reading about how particularly devastated John was.