Poor guy. He's still quite young, relatively speaking. Cancer is a real bitch, even after the disease itself has gone.
So I wonder... what will happen in 6 months time... he likes to keep himself to himself so will we be wishing him well on his trip to the great Apple in the sky, or will he do a Jesus and come back fit as a fiddle and all like "behold, I have been reborn"? The latter suits his character, the former suits the sad reality of life. Pretty much 50/50, IMO. We'll have to wait and see.
Best wishes to Steve and his family.
P.S. Those who are saying that if he leaves / dies Apple will fail. No. Yes, it'll be a very sad event and they might struggle for a bit, and whilst you can replace a position you can't replace an individual like that. But I'm sure the other managers of Apple haven't been sat on their thumbs learning nothing all this time - he'll have taught them a heck of a lot.
When Steve went the first time, it was due to some arrogant backstabber (that he hired!) who wanted him out and effectively sacked him, and started taking the company his way. The wrong way, obviously. I doubt they'll make the same mistake twice.