A whistleblower is the type of person to refuse such an NDA, regardless of buy-off price. They would understand that if Boeing is willing to pay them 10 million or whatever, that the information they have, should they release it, prevent over 10 million dollars worth of damages to the public.
I just don't see someone like that committing suicide in a hotel parking lot out of state the day (two days?) before they are supposed to testify. That would go against everything they were doing up until that point.