Trump and Pence’s current terms expire on Jan 20th whether there is an election or not.
House terms expire Jan 3rd, as do terms for a third of the Senators, Governors, whatever are still in office on Jan 3rd can fill the vacant seats I guess.
So Acting President would be a fight between the Pres Pro Tem of a possibly Rat majority mystery Senate and Pompeo, the Sec of State. Without a House there could be no legislation passed.
Everyone would be in so much panic produced by the MSM nobody would care who’s in charge.