Short of full-scale nuclear war, I doubt anything manmade would stop an election. Disrupt or delay counts, yes. Stop, no.
Remember each state has it's own voting system, that decentralization is actually not a bad thing.
An extinction-level event, like a super volcano eruption, or catastrophic meteor strike....well, then all bets are off.
If they can delay the count or certification long enough - pass the inauguration day, what then?
We're not as divided as we've ever been but we're getting close.
