I don’t think there is a strong case to be made that the CEO matters much here. We’d need to see the counterfactual of what would have happened in her absence. Maybe the same, maybe better, maybe worse.
And in any case, there is no reason to believe that Yahoo’s or any tech company’s continued existence is normal. Yahoo was of a time, as was Digg, MySpace, etc.
It’s easy to say they “screwed up”, but success for any amount of time is the exceptional part. Regressing to the mean of “non-existent” or “not valuable” is…normal.