Oh the Irony! I bet they wish they took the 45 billion 8 years ago.
AOL was worth $4.4 billion to Verizon, and was worth several billion publicly traded. Yahoo's operating business is blatantly worth more.
Simple test: show me one example in the last several decades, of a publicly traded company that was sporting a positive balance sheet, with billions in revenue, that traded with a negative market cap. You won't find a single example. It's also the same reason Yahoo didn't trade for a negative valuation prior to Alibaba becoming highly valuable: Yahoo's core business is actually worth something.
Microsoft and others don't seem to know what they are doing.
Management != the shareholders. Just because the right thing for shareholders is to sell yahoo doesn't mean that management will go along with it.
THAT is why the core business is worth negative 5 billion dollars. Because management will do everything to drive the company into the ground in order to prevent themselves from loosing control.