"He didn't disappear - well not entirely, he couldn't remember the password to that YouTube channel where he uploaded those videos. He has since been uploading again."
His original channel with the 4th dimension video:
https://www.youtube.com/@xkcdHatGuy/videos
His current channel, similar name, same guy:
https://www.youtube.com/@thexkcdHatGuy/videos
He also explained his 'disappearance'