Tupac was a dunce... his "music" (a.k.a. expensive karaoke) is and always was terrible (although a few were catchy, probably from the loops he stole from other musicians) and his fans are all knuckleheads. All of them.
Kurt Cobain was idolized before and after his death. His suicide was the healthiest thing to have happened to his career as far as his legacy is concerned. Grunge was on the way out, Cobain's buckshot or not, and he knocked himself off as the rollercoaster paused at the top of the track. He would have released terrible albums, no doubt about it.... Look at Pearl Jam. If Eddie Vetter had hung himself from some rafters the day after Cobain put lead through his head they'd both be remembered as angels. I loved Nrivana back in the day, and I still listen to them occasionally... but Coabin bled that scene dry.
Elvis is overrated. Way, way overrated. He was the Eminem (and this is coming from someone who thinks Eminem is a walking ball of douche who gets paid to create unlistenable douche noise) of 50's and 60's Rock and Roll. He repackaged an existing flavor of music for an audience with lots and lots of money, and he's remembered as some musical prodigy. If he continued to live any longer during his fat, drug-addicted slob period he would have begun to taint his legacy. For Elvis fans it's probably best that he died when he did, although sooner would have been better I suppose.