Robin William's suicide was a shock to most people. A person with depression who considers suicide and talks about suicide as a possibility is hard to comprehend. Perhaps that's why my relatives weren't prepared when he gathered everyone and said goodbye. Many relatives were professionals but ASKing didn't happen.
So now I am especially, strongly suggesting going to this app or one like it. Anything that helps you talk to someone who is extremely depressed. You can download the app beforehand and have it with you when needed.
How to: go to the App store and search "suicide prevention ASK by Mental Health of Texas". This app has warning signs and very clear questions to ask. It takes some maneuvering to get to the Ask questions. (Using the section Ask:Here's How, keep swiping 3 times to get to specific questions, it does take some persistence).
As a therapist I know people do Want to be asked. They are not insulted. They want others to reach beyond their comfort zones as a sign of love for them. Couples need to ask each other, family members, in-laws and more. Being a professional is not necessary. As a starting point to help a depressed person, please ASK.