Sad to hear this. His personality and voice had a way of invigorating whatever he was talking about. He managed to remain positive and constructive yet not come off as pandering to rock stars. The guy was a good conversationalist and didn't appear to depend on scripted questions. His legacy is a great contribution to documented music history.
He has been fighting for a while now. They had a benefit ride and concert for him a few months ago, but he didn't like it being called The Ride For Bob. The show featured Taylor Hawkins' band Chevy Metal and guests sitting in. Bob did his daily morning show on KLOS whenever he felt up to it right to the end. They have a tribute page for him on Facebook.