Jack wasn't doing well last time I saw him (about 6 months ago). He had pretty serious surgery (think it was ruptured colon) & Great White was doing a show in Ga. Jack was having trouble with most of the songs. I heard Jani Lane replaced him on their tour soon after that.
Man, I'm really sorry to hear that. I knew Jack back in the early 80's but completely lost touch once they got signed and released the first full length album.