According to a regulatory filing, Marissa Mayer won't be part of Altaba when the Verizon Deal closes on Yahoo.
Altaba being the remaining business.
The filing also doesn't indicate whether Mayer will remain with the acquired side of the business after the deal is closed.

Mayer will receive a severance package worth about $23 million, the filing says, if she's fired without cause or leaves the company for a good reason. Marissa Mayer Won't Be Part of Altaba After Verizon Deal [uk.businessinsider.com]