President Trump’s COVID-19 diagnosis, and the risk he might have spread the disease to Joe Biden at the debate, raises the interesting procedural question – what happens in our system if a candidate dies late in the election cycle? There’s a short, simple answer.
Death of a Presidential candidate, before about mid-September, would trigger a brief emergency in which the national party would be forced to quickly nominate a successor, probably whoever had been the original VP nominee. After mid-September it would be too late to get a new candidate on the ballot. As of yesterday, October 2, more than two million Americans had already cast their votes. In that case, the deceased candidate would remain on the ballot. If they won, the Electoral College would name them President. In January, the Vice-Presidential candidate would take office as President and select a new Vice President.
Things get weird if both the President and Vice President on the winning ticket die before taking office, but that remains a very remote possibility. In short, the death of a winning candidate has little impact on the final outcome beyond its potential influence on voters.