“What are the faithful at risk of?”

For one thing, they're at risk of directly or indirectly transmitting a dangerous virus to vulnerable people who didn't attend church. Getting our fellow citizens killed isn't Christian charity. It's a scandal that will drive people away, or further harden their hearts against Christianity.

Can the contents of the chalice transmit contagion? We're taught that they cannot. I accept that. However, standing in proximity to an infected person for a couple hours, touching what they have touched, etc. could certainly result in illness.

Do we think that respiratory illnesses can be transmitted at all during an Orthodox liturgy? Is there any evidence for that? It would certainly be a testable hypothesis.