I haven't seen the details of UD's arrangements, but in the case of MIT yesterday, they explicitly provided an exception for students who didn't have any other housing to return to. It would be a sign of extraordinarily bad management at UD if they didn't provide the same.
> This seems like illegal eviction to me.
I discussed this in the MIT thread yesterday, but contract law does provide mechanisms for invalidating or modifying existing agreements under extraordinary circumstances. The doctrine of force majeure (https://en.wikipedia.org/wiki/Force_majeure), for instance, under which both parties to a contract can be relieved of their obligations if some unforeseeable, unstoppable outside force makes it impossible or impractical for them to meet them. American contracts commonly have a force majeure clause included with the rest of the legal boilerplate.
One potential wrinkle here would be exactly what legal standard would be required for the coronavirus to qualify as a true force majeure. Massachusetts and Ohio both declared states of emergency due to the coronavirus yesterday; I suspect it's not a coincidence that universities in Boston, MA and Dayton, OH waited for those declarations before they started taking these types of actions.