Well chances are they have a plan B if they delay this movie, hence why the ticket selling was withheld. Of course no one is gonna bring the doom and gloom at a shareholders' meeting. But I noticed USA gov't as a whole has yet to press the panic button. Events are still pushing through in most States, so why would the Disney board not placate its shareholders?
Mulan was unlucky with its schedule, but companies already are anticipating big losses this year, tourism the most. If they choose to stagger their releases, then they might at least not bomb the movie. Guess we'll just see how it plays out.
Edit. Closing of the Disney parks in Asia were done when the governments ordered everything to close. We'll see how USA handles this thing.