Valid or not, you don't blindside major investors who have given you billions. They apparently told Microsoft minutes before the announcement and after the decision had already been made. Even if you fully intend to take this course of action, you loop in your major investors and consult them or at least give them a heads up to prepare any communications they might need to make or even just their press people are prepared for the inevitable questions.
They didn't do that, according to Micrsoft. That's why they need to be fired.
And MS isn't an investor in the company of the board.