So the guy goes on for years being an outspoken whistleblower telling his story to anyone that would listen, and decides while in his hotel waiting for his deposition that now would be the best time to end it and not move forward with holding Boeing accountable.
Occam's razor isn't pointed in the direction you think it is.
I mean, you are welcome to believe that, but if I was a betting man (or had money to bet), I doubt the company had him killed.
Corporate malfeasance, even that kills people, is rarely likely to put people in jail and executives are still likely to end up wealthy. Conducting the most obvious corporate assassination possible under extreme public scrutiny would lead to criminal prosecution of individuals that would definitely result in prison time.
Meanwhile, suicide is extremely rarely logical, and people who end there often were anywhere from having their entire future ahead of them to being amidst some of their most profound success.
Occam's razor isn't pointed in the direction you think it is.