As the status quo seems unlikely to have a catastrophic turn for the worse

Neither of us is qualified to judge whether that's true.

The fact that you talk with this person exclusively over IRC limits your options a little, but it also changes things in one important respect; it greatly increases the probability that you're the only person (or only responsible person) with this information. He might tell you things that he doesn't tell any of the people he interacts with face to face. If you're the only one who knows, then you can't just sit on that information.

If you do call a hotline, the first thing they do will probably be to find out who your friend's psychiatrist is and contact them. The information you have is sufficient to do this discretely. They are well aware that doing the wrong thing could be disastrous, and aren't likely to do anything stupid.