If they did manage to "gut" the house and senate, do you honestly believe they would've just stopped there? Just shrugged their shoulders and said "ok, welp nothing we can do. Joe biden will still be president!" No. The only person with any authority left would be Trump.

Yes, but only because there would have been no one else left.

They are constitutionally required to certify the results. Section II of the constitution lays out that they count the EC votes. The winner of the majority will be president. If they don't have that count, or if they are all murdered, who is going to tell the sitting president he has to give up his power if he doesn't want to? Again, we would be in an insurmountable crisis.

If there’s no quorum then they cannot, and you wind up with Acting President Pompeo from the 20th until Congress is reconstituted and certifies Bidencas the winner.

These are very simple answers, and you’re really reaching here to support a poorly thought out comment.