Rather than the inevitable bashing of Marissa that will undoubtedly unfurl on this thread, I'd like to put in a little reminder that we usually celebrate taking on big projects and big risks and that we should commend her for taking on the immense challenge of steadying the Yahoo ship. Yes, she wasn't able to keep the ship from sinking. But I do think she put in a good-faith effort.
I do as well. As outlined in The Halo Effect, people want very tidy, clean, and rational reasons why a company failed. Blame must be specifically laid somewhere. However, there's a pretty good chance no one available could have saved the demise of Yahoo. Variance is a thing.
Case in point. A clean, tidy, rational reason why Yahoo failed: it was impossible to save. Blame the company itself.