New York 9/11 election:

I am told that when the New York election scheduled for 9/11 was postponed, the votes cast on the original day were discarded, and people were expected to revote on 9/25. Joel Graber, of the New York State AG's office, posted something more about this to an election law list I'm on, and I pass it along with his permission:

In New York City on 9-17-01, nine African-American, Hispanic and Asian-American Democratic candidates for City Council, and some voters, represented by highly-experienced civil rights attorneys, sued in the EDNY to postpone the primary rescheduled from 9-11-01 to 9-25-01, alleging violations of their "right to vote, free speech and political participation, freedom of association, right to due process and equal protection of the law," and sections 2 and 5 of the VRA. The claims boiled down to the arguments that the board of elections, which is located close to the WTC, was not up to the task, that voters were too distracted by the attack, and that Rosh Hashanah fell on Sep. 18 and 19 thus hampering plaintiffs' opportunities for political activity. A [temporary restraining order] and [preliminary injunction] were denied by [district judge] I. Leo Glasser on 9-20 and the case was abandoned. Barbour v. Board of Elections, EDNY 01-cv-6216 (ILG).

Legislation was passed on 9-13 resheduling the primary (and liberalizing absentee voting and other things), on the authority of N.Y. Const. art. III, sec. 25, which provides that the Legislature, "in order to insure the continuity of state and local government operations in period of emergency caused by enemy attack or by disasters (natural or otherwise), shall have the power and the immediate duty . . . to adopt such . . . measures as may be necessary and proper . . . ." The legislation also provided that valid absentee and military ballots cast by 9-11 would be counted and that votes cast at polling places on 9-11 would not be counted. 2001 N.Y. Laws ch. 298, ch. 303.

So at least in New York, there is already state law authorization for the state legislature to take care of election interruptions.