I just feel like there's something I could have done, or that the group could have done, so that he didn't have to die.
I hear where you are coming from, sixyearsober. I can see from your last post that this is coming from hurt in losing this dear friend, not an attempt to be an honesty cop.
I sometimes think about this misguided idea that those with long term sobriety just don't get down, or don't have problems and are held up to higher standard than those with much less time. I know I fell for that early on in my sobriety, as I rarely heard an old timer discuss anything going on with them....mixed with my own wrong image of what an oldtimer is supposed to be "like". I say this because I wonder if your friend felt that he had to live up to a status that no one can? We don't know, he can't tell us. But who knows -even if the culture of the group was of pure honesty - would that have helped? Perhaps he wasn't even honest to his own sponsor? Who knows.
miamifella said it well - something to foster. It can start with the newcomers too - encourage them to be honest from the start, show by example, etc.