Iirc, in one of his last public appearances before abandoning Kbin was commenting he had health issues.

Just noticed he has a blog where he occasionally posts, latest post being from September, and in the "about me" section, he also mentions about having to drop Kbin.

Going by his posts and his repositories, he doesn't seem involved with ActivityPub anymore, at least in a public manner. But sharing in case someone worried about the person.