To answer your question: Number 1, we don't know him personally, but DarkStar has been here since 2015; he's quite popular and trusted here on Bitcointalk, just so you know. As far as I know, he rarely manages signature campaigns because he focuses on managing the Chipmixer signature campaign. Number 2, he didn't disappear; he's just taking some rest, as he stated in his signature space. He might want to not get involved in what's happened with Chipmixer.
Regarding Chipmixer's owner and the situation happened to Chipmixer case, this article might help to answer you question:
Germany and U.S. Seize Over $46M Crypto Tied to ChipMixer InvestigationI don't understand why this post gets merits. I can see myself that he registered on this forum in 2015 and I can see that his trust rating is very high but my question is, why did Chipmixer choose he for signature campaign when there were many other experienced signature campaign managers? I bet he was one of the least experienced one but correct me if I'm wrong here, don't know well what was happening years ago.
Is he really just taking some rest? Because he has an active loan giveaway thread and doesn't even care about active loans or am I wrong?
I am not doing any investigation, just wondering why did he disappear, is he really afraid that his connection with owners may cause him trouble? Because this definitely is not a rest. Hope everything is all right.