Besides the fact that proving guilt has nothing to do with whether a business retains a person, but the scandal is enough that it can bring enough of a negative image to the proceedings to hurt their continued profits. Besides the fact that is the exact opposite way slander works, Slander is only when the statement is proved false, not until it is proved true.
But as a business perspective, Sony had no choice in the matter. Scott did this, on his own. and now the film has turned negative buzz into positive buzz building up into award season. And will probably make more money now then it would have a week ago, or even before the accusations against Spacey.