Mal, Lester Bowie, Sam Rivers, Elvin, Max, Roy, Motian spring to mind.
Max canceled a gig I had tickets to and the decline in his health had presumably started.
Roy and Paul were just on account of my own error. Mal, Sam, Elvin, and Lester just did not happen for whatever reason.
I'm pretty lucky to have seen a lot of greats given that I'm relatively young in age.