Within the challenge of talking about mental health, there may very well be people in need of immediate help. Is there anything we can do to make sure that if people come to this site in desperation, in physical danger, they can get the emergency help they need?
People who are considering an action that will harm themselves or another have been known to reach out to internet communities. Lives have been saved by posters contacting local law enforcement. That said, this is so serious that any official policy will have to be reviewed by SE's lawyers. But, I propose the following
User flags the post. This should be it's own flag. Example:
...it is a threat to the health and safety of the poster or another person.
Moderator reviews post and forwards notification to SE.
The poster's IP address and the content of the post should be forwarded to local law enforcement if possible.
The post should be locked while the content is under review and, after the review is completed, the post should be deleted.
There are two outstanding issues. First, even if the user thinks the post is a troll, it should still be reported. SE staff needs to decide how to handle it. Second, it should be made clear the consequences of making a false threat or responding inappropriately to a false threat.