To me that sounds like the wrong person to bet my money on. The employee who plays it safe is not right person to transform a dying company that needed radical change. You need a bolder person. Someone with a burning passion or an act to grind.
If you are google employee 20 and you haven't cashed out to build something you always wanted to but didn't have the resources yet I don't think I want you leading the transformation process. I would rather have employee 21 who quit and tried something else and failed.
By her own words, she thought Google had a 2% chance of success. Is that not enough risk for one life?
http://fortune.com/2011/10/03/marissa-mayer-i-thought-google...
Also, her experience running hundreds of projects and experiments at another billion dollar tech company is exactly what they wanted. Not whether she does all-nighters and knows Rails. I'm not going to argue that the Yahoo board made the right choice, but you would definitely have made the wrong choice.
I was optimistic when she came on board, because Yahoo really needed a strong product vision and someone who had a touch of ruthlessness. But maybe it was unsalvageable.