> Imagine the legislators didn't escape - that a majority of them were killed.

Less bloodily, imagine the boxes of electoral vote certificates didn't escape in the hasty evacuation, and the certificates from th contested states were selectively destroyed, so that when the session was able to resume and the certificates were counted, they weren't present. (Remember that a recent public scheme to overturn the results was a campaign to simply have Pence not open the certificates from the states whose votes Trump disputes toe exclude them from the count.)