Congress is killed. What happens?

[Vosem]

I think it would be a reasonable fudge if a majority of the House of Representatives were killed that whatever survivors happened to be out of town would be able to rewrite the rules to declare themselves to be a quorum, or even a majority (amusingly the likeliest reason for someone to be absent is medical treatment, so we could be stuck with a disproportionately old, sick House...). Much of the regular business of the House would ground to a halt but urgently necessary legislation could still be passed.

The same would be true for the Senate in the immediate aftermath of the attack, though it would quickly be refilled, since most states permit Governors to appoint whoever they want and there would be a clear both national and state interest to fill those seats as quickly as possible. Without much time to interview possible replacements, I could see the new Senate quickly fill up with Carte Goodwin/Jeff Chiesa types (convenient, trustworthy lackies of incumbent Governors) until the next elections.