What should happen if there is a major terrorist attack on election day?

[HeldsBelds]

Let's say there is an attack on the scale of 9/11 in a major metropolitan area and voting is disrupted.

The county or state where the terrorist attack occurs declares a state of emergency and orders its poll workers to leave the stations for their safety and people are thus unable to vote.

How does this situation get rectified? Will the elections be cancelled and re-done on another date? Isn't the first tuesday in november a constitutionally mandated date which would make a re-do impossible?