I'd ask them what is the root of their depression? After all, that emotion is something quite blinding and NO MATTER what I could tell them unless they worked through their agony they could better their overall situation. Suicide is a deep cry for help. It's something that happens to many and it takes great strengths to overcome. Of course, life isn't easy, to live is to battle the many obstacles that may be. Of all the downfalls and tribulations, one thing is true that no matter how dark (there will be a light or glimmer of hope eventually). You just have to try something new, because in life anything is possible.