Your question is flawed in several ways.
There is not one general election. There are 51 elections, one in each state and one in the District of Columbia. Each of those elections is run by a state or the district. That means the laws of each state and the district applies to its election. There are 51 answers to your question.
In most states and in the district, it depends how far before an election a candidate crumps. The general rule is that if the candidate crumps before the ballots have been printed and distributed, the party can substitute a new candidate.
Another flaw in your question is that you seem to believe you actually vote for the POTUS/VPOTUS. You do not do so. You vote for a slate of electors pledged to vote for the POTUS/VPOTUS candidates put forth by the parties. Those electors vote for candidates when the actual POTUS/VPOTUS in the presidential election which is held in the state capitals on the same date in December. If a candidate crumps between the 51 elections in November and the electors’ casting their votes, the electors can vote for a living individual (who will probably be “approved” by the party whose candidate crumped.)
By the way, the answers to your flawed question are contained in the Constitution of the United States of America.
The question wasn’t about what the Constitution says, because it is silent on the nomination process, except for candidate qualifications to hold the office.
The question was about what happens before the ballots are ever cast if a candidate became incapacitated or deceased. Presumably, the Electors cannot pick someone unqualified under the Constitution, and being dead or incapacitated are specifically mentioned as disqualifications.