You can handle it a number of different ways. However, it is best not to tell anyone else. Gossips, even if true, are not looked at in a good light by corporate managers and executives. Best way to handle it is to say nothing and keep working hard. If your boss is terminated this means they will be bringing someone new in, or promoting from within. Either way, you will either have to prove yourself to the new manager, or prove yourself to be a good candidate for the managerial position. Work hard, be smart, and have a good attitude.