His voice isn't shot, his range is diminished though. There's no way he'll be able to sing the Soundgarden classics in the original key with the original melody when they tour. His voice is comparable with Plant's in the early 90's; still a great singer with a unique and instantly recognizable tone and timbre but with a range that's been reduced from his former bands "glory days." And to be perfectly clear, I'm not bashing Cornell. I still love his voice.
He was singing a lot of the Soundgarden classics on tour with his own band just last year, same key as originally. Plus screamy classic covers like Zep's Immigrant song. I don't think his range has diminished much, if at all.
Jesus Christ Pose
http://www.youtube.com/watch?v=2eje0eZDHpMImmigrant Song
http://www.youtube.com/watch?v=G9OLBoa8IXc