Mental illness and depression is not talked about very openly, but it was definitely not talked about like it is today. It is good that people are coming forth and discussing it, instead of holding it in and having it come out when they get home and they go inactive.
Unless you were in position to actually know why someone went home, such as a companion or Mission President, you would only be speculating it was a moral or other issue. We were taught to endure to the end, and is was absolutely taboo to admit depression or anxiety, let alone openly speak of it. It was just as prevalent in 79 when you were serving and 98-2000 when I served, as it is today. Having a retired Medical Doctor as our Prophet is also affecting certain aspect, because along with revelation, he also understands the psychological issues and studies of what is effective in helping the missionaries.