I've had the chance now to talk with the sister of argon_centaur and to get more information about what's happened. I'm sorry to report that the news we had gotten was correct. He did pass away just before Christmas.
In May he had disappeared from the online world for several weeks in what we thought initially was a side effect of flooding where he lived, and then heard was a stroke, and then learned was a less serious medical crisis. The third report was, it appears, Argon trying to make the news less grim for his friends. He had suffered a stroke, which in collaboration with his diabetes left him not really able to live on his own, which is why he moved up to be with his sister. She believed he was growing comfortable and reasonably happy there, being closer to family, and even getting unexpected surprises like seeing a real-life bear in the driveway.
He'd since suffered a number of problems keeping his blood sugar level in control, and this December he suffered either another stroke or a heart attack. His sister didn't want to know and didn't think it very important to determine.
He passed away while his sister, and family, were visiting other family for the holiday. He was very clear in wanting to let them go without him. When he missed his regular calling-in his sister phoned an emergency medical technician friend, who found him. The friend reported that his death was peaceful.
Argon's sister asks that the news be passed on to his friends' circles. She has almost no idea of his online friends --- she said apart from his best fiend she had ``no idea where his friends were'' --- and their social circles, and has only just been able to go into his rooms and turn on his computer, which she says has not been cooperative.
We will hold a memorial service when we've had time to organize it properly.