He is successful enough, old enough and made enough money, that he can just retire. Threatening him is an empty threat. He is 60 and probably given his long career earned more than he can spend in rest of his life, unless he goes super yacht and private jet crazy.
The whole show was a come back from retirement essentially. A voluntary indulgence on his part. Surely lucrative indulgence, but indulgence still. Apple needed him, he didn't need Apple.
Most of the crew probably will leave for other project with a letter of recommendation from John in their pocket.