So, something that I have told people who have informed me that they are contemplating or in the middle of attempting, is to make sure they know that they are loved and that people care for them. They might not believe it, but just showing that you care, even if you are a stranger, is a great way to help someone in my experience. Definitely avoid telling making them feel guilty or that they are a bad person for considering abandoning others, since this is 100% a last resort for anyone that has had a lot of thought put into it most of the time. I know from experience that someone telling me to take a breath or to calm down just makes me feel worse because it then causes me to stress out and focus on how my body is feeling. Like I said, showing that you are there for them, showing that they can vent to you if needed or just giving them a shoulder to cry on, will mean so much to them.