I’m not sure what this buys them, since a lot of the value in what they have left is name-based. If people have several dependencies on Yahoo.com E-mail addresses, they won’t want a “new” free E-mail with a different domain. People already know names like “Yahoo Finance”, etc. and any other name will throw that easy recognition away. And don’t even get me started on what “Altaba” is supposed to be (I’ve already mistyped it about 3 times trying to write this comment).
Since everybody here is confused on why they would give up the Yahoo brand: This is not the Yahoo which was sold to Verizon (which stays Yahoo, incl. email service) but the investment vehicle holding all the Alibaba shares. The name "Altbaba" is an obvious play at the official ticker of Alibaba (BABA)