My guess is they have, just not publicly. (Easy to argue the merits of that.) Pancreatic cancer doesn't leave too many survivors so I am sure the management team thought a lot about life without steve, at least at that time.
I agree, but I think it's less of an internal logistics issue and much more of a public image issue: Steve Jobs is so much the face of Apple as it sits currently, every time there's news about his health the stock fluctuates and that isn't good.