Explain that suicide might cause them to miss out on a Utopian Singularity.

Don't. Unless they are already Singularitarians. You'll just come across as weird.

MoreOn: I have no idea what you might say, but unless you are close to both of them and know their circumstances well, I don't see how you could help. (I'll be watching the thread to see what others have to say.) How out-of-the-blue offers of advice or help from near-strangers are taken will depend a lot on their current mood and unless you can accurately read that I'm not sure you would be doing much good. Of course grab all chances that present naturally to be nice and supportive to them, maybe motivate common friends who are close to them to talk to them etc.