"spy CEO" wasn't my original intention. More like "figure-head whose intention is to benefit Google and whose loyalty is still with Google". Google's leadership is very shrewd and it would be foolish to blindly put this past them.
To be fair after reading a bit more and thinking about this it could be a vanity move motivated by the promo skip.
I'm sure Marissa's departure was considered a huge loss at Google, especially to go to Yahoo. No company is ever happy to lose an executive.