Nope. I would not step in. That's his to do. Needing to talk to you ASAP could range from "Please let's put the sheets back on the bed" to "Let's go to my friend's memorial service, can you get off work". Really. The nature of your post indicates a little bit of panic on your part. Depression, while it can be serious, is treatable. He's been treating it for 2 years. If, for some reason, his meds aren't working, he knows it. He knows his doc's contact information.