How much could Marissa Mayer get if she and Yahoo part ways?

Yahoo Chief Executive Marissa Mayer was not only the highest-paid female CEO last year, she was one of the best-paid CEOs overall. Depending on which ranking you check, her $42.1 million in 2014 compensation notched her as the 23rd, the 14th or even the fifth most highly paid CEO of a major U.S. company.

So as questions swirl over Yahoo’s future — the company’s board said Wednesday that it had scrapped the idea of spinning off its stake in Chinese e-commerce giant Alibaba Group and will examine a “reverse spinoff” of its other businesses instead — it’s not surprising that many people are looking to see how much Mayer could make if she and the struggling Internet pioneer end up someday parting ways. “$157.9M!” blared a USA Today headline.

Although many “ifs” remain, one thing that does appear pretty certain is she wouldn’t walk away with nearly that much.

In Yahoo’s most recent proxy statement, the company estimates the potential value of Mayer’s “change-in-control severance benefits,” as of Dec. 31, 2014, at $157.9 million. That’s the value of what Mayer’s package was estimated to be if she was terminated without cause and if there was a change in control of the company, such as a sale or merger.

Meanwhile, the most recent company filings put the value of her estimated severance benefit at $36.1 million, which is what she would get if she was terminated — again without cause — in a scenario where there wasn’t a change in the company’s ownership.

Yet at nearly a year old, those figures are now way off. That “golden parachute” estimate is about $100 million lower, according to the number crunchers at Equilar, an executive compensation research firm. They estimate — with the caveats that there are a lot of variables involved — that the figure is closer to $59.3 million now. Another analysis by Bloomberg put the potential package at $35 million.

The current value of any potential severance benefits, meanwhile, is more like $23 million, Equilar senior research analyst Courtney Yu said. (A Yahoo spokeswoman, reached via email, declined to comment on Equilar’s calculations.)

Here’s why: For one, Yahoo’s shares have fallen roughly 30% since the end of last year, when its stock was worth $50.51. Since the largest part of such payouts is made up of equity grants — whether in the form of options or restricted stock — that significantly lowers the value of any potential soft landing.

In addition, equity awards usually vest to executives over a period of several years, with percentages of the total grant becoming available over time. So more chunks of Mayer’s equity awards — especially some from a particularly lucrative retention grant she received when Yahoo lured her over from Google in 2012 — vested during the last year. As a result, she now owns them, lowering the value of any potential parting gift if there’s a change in control.

Still, even at $59 million, that potential change-in-control severance package is quite high. If she were to end up getting something that size — and again, that’s still a very big if — it would be the 10th-largest payout among large companies over the last 10 years, according to Equilar’s data. The largest, paid to Gillette CEO James Kilts in 2005, was $164.5 million.

Change-in-control severance payments skew larger than regular executive send-offs for a reason. As with Mayer’s awards, most boards allow outstanding options or equity grants to be immediately vested, or accelerated, if there’s a change in ownership. That’s to keep CEOs from thinking with too much self-interest about all that stock they could be leaving behind, rather than about what’s best for investors.

“It’s to provide the executive with a fallback, with an incentive, to act in the best interests of the shareholder,” Equilar’s Yu said. “The company wants the executive to not be afraid to potentially lose” out on those awards. Still, say Yu and Paul Hodgson, a partner in compensation research firm BHJ Partners, these packages are large enough that a few investors have begun pushing back and trying to limit how much stock is accelerated. They’re saying “enough of this, we’re tired of paying for everything twice over,” Hodgson said.

In Mayer’s case, any potential package is likely to be bigger because she was a star hire recruited to a struggling company where she is still relatively early in her tenure. Again, all of this hinges on a number of big question marks. One, of course, is what the board ultimately decides to do, and if there is an eventual sale, whether Mayer will actually go anywhere. Then there’s the question of what would constitute a change-in-control at a company like Yahoo, which holds such a big stake in Alibaba Group.

If in fact all those “ifs” transpired, and Mayer ended up with the $59 million that Equilar calculated, she would have some interesting company. The figure is not far from the $58-million severance payment given to Mayer’s former deputy, Henrique de Castro, who left Yahoo last year after just 15 months.

McGregor writes for the Washington Post’s On Leadership section.