Ian Abercrombie's last major credit was as the Headmaster in Wizards of Waverly Place, which just wrapped up a few weeks ago. This is the second time in recent memory that Disney's wrapped up one of their shows, only for one of the big stars to pass away a few weeks later. The first case was with The Emperor's New School, where the show wrapped up and Eartha Kitt passed on weeks later. It's a very odd coincidence.
As JST alluded to, he also currently leaves Star Wars: The Clone Wars without a Palpatine. He was awesome in that role.
Nitpicky: Weren't their names on their Twitter accounts? If Brian made a big deal out of noticing no pictures of himself in Quagmire's house, how come he/everybody failed to notice he was in some framed Griffin house photos?