No 2020 Election?

I've been asked what happens if the US doesn't have a Presidential Election in 2020. First off, only Congress can officially change the Election Date (which has never happened since the country was founded 244 years ago - even during the Civil War, the 1918 Spanish Flu Pandemic, the Great Depression or World War 2.) Second, if the US doesn't hold a Presidential Election in 2020 then on January 20, 2021 -  Inauguration Day - Trump is officially no longer the President and Pence is officially no longer the Vice President. That means that until we hold a Presidential Election the Interim President would be the Speaker of the House of Representatives (Nancy Pelosi) and no one from any Party wants that.