That is correct.
There would be a vacancy for that riding.
As I said, it's a practical test. Can I offer voting services? Do I have access to polling places, to poll workers?
In all likelihood, if there were an extreme case of a shutdown and people were told by public health authorities to stay home, then that would prevent me from having access to poll workers and offering services to voters, who would be largely at home. That's a very extreme scenario.