Senate is easy, Governors appoint interim picks. House seats, not yet sure. That said, IF some of the Governors are arrested and even SoS critters, the line of succession has to kick in and I am not sure how this all plays out. Its a state by state, of course, but not a day or two job as some make it sound. It may take some time to reconstitute Congress until next election takes place. In red states it should be easy. In blue ones its a crap shoot right now, IMO. What's the point of cleaning the Congress if blue states simply send more rats in?

Need to research the Constitution a bit to see if there is a provision for such an event, and if there is a minimum number in Congress that makes it operational on interim basis. Its certainly a mess.