I just don’t see litigation:
1) If someone goes to WDW they are going voluntarily and they know the risks.
2) How do you definitively prove the person caught Coronavirus at WDW?
As a lawyer, I see similar litigation all the time. Earlier in my career, I did some work with Asbestos litigation which was even broader.
If you got lung cancer... you could sue employers from 10 years earlier, if that employer 10 years earlier exposed you to asbestos.
That you were exposed to asbestos.... and that you later developed lung cancer, that was enough to establish that the asbestos at the job caused the lung cancer.
People "assume risks" and still retain the right to sue all the time. If you go to the grocery store, you know there is a risk of spilled messes in the aisles. But lawsuits of slipping on spilled messes are extremely common.
So applying this to Disney:
If Disney has a mini pandemic... a couple hundred people get infected from Coronavirus, showing symptoms 5-10 days after being at Disney World... a dozen of them die..... That would be ample proof that they got the infection at Disney.
You don't have to prove beyond a reasonable doubt. You just have to prove "more likely than not." Basically, if there is a 51% chance you got the infection at Disney, then that's enough to win a case against Disney.
But then we get into knowing the "risks."
Let me get to the supermarket example:
If a mess gets spilled, but there is no policy of quickly cleaning it up, placing cones around the mess, etc... then the grocery story will face liability. If a kid knocks over a pickle jar, it breaks and spills, and someone slips 3 seconds later... The grocery store will not face liability. The question is whether reasonable steps were taken. Bad things can happen even if you take reasonable steps. But you have to take the reasonable steps to reduce risk. That's the legal standard of care.
Applying this to Covid:
What are other institutions doing to reduce Coronavirus risk? We know theme parks in China are requiring temperature checks, they are requiring masks, closing high density attractions.
If Disney decides to maximize profits by packing people in like sardines, while their own internal health care advisers are warning of health risks, then they would face enormous legal exposure.