I'm a little skeptical as the main source of this info is him, from his twitter feed. He is totally the type of person to make up an illness to create a distraction... maybe take the news off the debate and maybe hope to get some sympathy. I could even see him lying, just to show up a week later and say "see, i got through it, it wasn't even that bad!".
If it's true, I hope his death is long and torturous. Take Hope Hicks and your mail order bride with you.