Marissa Mayer’s three-year effort to turn around Yahoo has been a major-league leadership saga, as it was destined to be. Events of the past few days suggest – but don’t yet dictate – that the saga is in its final chapters.

Yahoo YHOO was a mess when Mayer left Google to take over as CEO in July 2012. At that time, no major troubled Internet company had ever been turned around, and this looked like as good a test as any of whether it was even possible. Mayer had been a star executive at Google and was widely hailed as a brilliant hire.

In a sense, she has done what she was hired to do, changing strategic direction and making bold investments. But the numbers tell the unhappy story of how her moves have worked out so far. Yahoo’s market cap is $31 billion. Its stake in Alibaba (acquired long before Mayer arrived) is worth $30 billion, and its stake in Yahoo Japan (ditto) is worth $8.1 billion. Apply some tax-related discounts to those values to reflect what the company could actually net by selling, and add $7.6 billion of cash and other current assets Yahoo held as of September 30, and we see that investors figure Yahoo’s actual businesses are worth approximately nothing.

That situation is not, as they say, sustainable. Fortune’s Erin Griffith explains how activist investor Jeffrey Smith’s Starboard Value Fund bought a big stake in Yahoo last year and reasonably urged Mayer to off-load its Alibaba and Yahoo Japan holdings so investors could buy or sell them separately from Yahoo. Mayer developed a plan to do so but ran into a problem: The IRS would not assure Yahoo that spinning off those investments in the way planned would be tax-free. Yahoo’s board decided the risk was worth taking and announced it would go ahead. Now, Smith has concluded the plan is too risky and is pressing Mayer and the board to do the opposite, sort of—sell Yahoo’s core operating businesses wholly or in pieces for whatever they might fetch, leaving Yahoo as merely a vessel for owning shares of Alibaba and Yahoo Japan.

Smith argues that, without such drastic action, Yahoo is in an irretrievable vortex of doom because it can’t attract top-level talent with stock incentives, since the stock’s performance merely reflects the performance of Alibaba and Yahoo Japan. Without the best talent, the company can never build its business to a point where it outweighs the performance of the Asian assets, leaving the company forever trapped.

Of course, Mayer disagrees vehemently with that reasoning, telling Wall Street analysts recently that the company is well positioned “to deliver long-term sustainable growth for our investors.” But investors have zero reason to believe her assurances, which is why envisioning any kind of long-term future for Yahoo is growing increasingly hard.

Maybe no one could have saved Yahoo. Or maybe Mayer still can and will. But how about this for a leadership challenge: One way or another, it seems likely that Yahoo’s businesses will soon be standing on their own, trying to persuade the world that they’re worth anything at all.

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