Actually, my Apple stock has been doing very well over the past few months.
Just saying... sure, Steve has some influence on the stock, but it's not as if Apple or it's stock survives off of him. When he leaves the company, the stock will go down - no doubts there. But it will rebound, and Apple will continue to be the great company it is today.
That said, I do hope Steve is doing well and finishes his recovery speedily.
The liver can regenerate but if you have irreversible liver failure, a transplant will be necessary. An entire liver is not required as a small portion/lobe of healthy liver can function adequately. I've heard that he has a rare (untypical) form or pancreatic cancer (although I don't know for certain what he has). Pancreatic CA is almost always fatal. IIRC, approx 29,000 of the 30,000 diagnosed annually will be dead within 12 months of diagnosis. The only people that survive it are those that get diagnosed in the very early stages. Most people aren't that lucky (like my Grandma) because the early symptoms are very subtle and ambiguous. The pancreas is so closely connected to the surrounding structures, that is spreads very rapidly. When found early enough, they do a procedure called a Whipple, nick named "slice and dice" and basically slice of sections of everything nearby the pancreas to hopefully stop the cancer from spreading. Liver failure has multiple causes and can be directly related to the pancreatic cancer.