Here's a list of who's gone insane or kicked the bucket:

Character Player What Happened Campaign
Nicholas Smuntz James B. Turned into a Deep One Hybrid, and later shot to death by Dr. Sotheby during the raid on Innsmouth Escape From Innsmouth
Mike Masrick Zero J Retired after losing his mind too many times Day Of The Beast
Dr. Richard Sotheby Eric F. Retired Day Of The Beast
Bruce Sotheby Zero J Cranium shattered from punch to the head by Baron Hauptmann Day Of The Beast
"Thug" Douglas James B Retired after losing a hand when attempting to punch an Avatar of Nyarlathotep Escape From Innsmouth