Can't see the major USA exchanges shutting down unless all the world's exchanges shut down. But the NYSE is preparing for such a contingency per news last week.

That could lead to quite a situation if they shut down for a couple of weeks. Might even be good to prevent major crashes until some word is given or things become a little clearer on just how bad this covid situation is to become.

What if in the meantime good news comes out regarding B testing?

Would make for some explosive movement once they open them up again.