Universal and Disney, and probably SeaWorld, are far too big to fail completely. Governments, local and federal, will not *allow* them to fail completely. The sick joke about this country is once you're big enough people are gonna do anything they possibly can to make sure you survive.
That being said, the ripple effect between now and a vaccine can still be devastating for Orlando at large. If the US continues to falter in containing the spread, especially in Florida, and other countries continue to impose travel bans on the US, many places around the parks will almost certainly close, which will increase the unemployment issue.