Actually that issue is already addressed in a couple of laws.
A law passed in 1845 marks the first Tuesday in November as the general election date. An older law in 1792 requires the general election to be held by the third Wednesday in December.
The 20th amendment of the Constitution also states if no candidate is ratified by Jan 20th, then the current sitting president and VP are removed from office and the line of secession will be followed.
End result if the election is cancelled Nancy Pelosi becomes president by default.