It would be taken down and I would send a message to the writer with mental health or counseling resources (ex: crisis text line). I take all messages seriously by default, even if it appears to be trolling.
If that person continued to write content like that, I'd do a bit more digging. This is where it'd be subjectively up to me as the moderator to take action. Banning or shadow-banning would be a last resort, generally.
There's no strong accountability on my end (beyond people not using the app), but I'm interested in creating a system people can trust. If the app continues to gain traction, I'm thinking about writing formal moderation rules and expectations and seek input from the community.
If you have any ideas, I'm eager to listen!