I’m a retired Navy captain (Surface Warfare Officer). I fully believe he had the best interests of his crew at heart. I also believe he knew he was putting his career in jeopardy by sending that letter, and skipping his chain of command. He had to know he could be fired for sending it, but he did it anyway, because he felt it was the only way to help his people.
I think he deserved to be relieved, and I believe he expected nothing less.
His career was ending and he got his resume out to the public just in time. Im sure some defense contractor will pick him up in short order.
I am sure that you are correct - he knew that he’d be relieved. Hard to find leaders that committed anymore. Hope he and the men with him who have that disease recover well.