In my opinion, no matter who the CEO is, Microsoft will go the way of the dodo. This because in the end they are not needed anymore. They don't manufacture hardware like Samsung and other companies do, and with things like Linux and Android out there, companies like Samsung (I use Samsung purely for example) can manufacture products with a familiar software environment and not have to pay royalties for it or require their consumers to buy a $99 OS. I think hardware companies are seeing this, and Android has already come to dominate the mobile space. It only is a matter of time before Linux does the same in the PC space.
Microsoft make most of their money from B2B sales and windows phone 8 is growing extremely fast. http://bgr.com/2013/07/09/windows-phone-russian-market-share/
Microsoft is kicking the crap out of Oracle, this is where most of their growth in revenue has come from despite windows server 2012 obvious flaws.
Microsoft is not a 1 trick pony and their share price always remains quite stable because of their diversification. They have tonnes of spare cash (not as much as apple mind) and a healthy balance sheet. They aren't going anywhere.