In short...
In October, especially later in the month, and in early November (before November 8), the situation would have become significantly more complicated. At this point, nearly all ballot certification deadlines would have passed, many ballots were printed, and voters in some states had already cast their ballots.
This begs the question: What happens if a candidate has dropped out of the race but wins the popular vote in a state? Would the replacement nominee just receive those electoral votes? The answer lies in what that state has to say about its electors in the electoral college. The Constitution does not dictate how electors must cast their votes. But some states do. More than half the states have laws dictating how electors must vote. If the former nominee won in a state that does not have a law on how its electors vote, then, theoretically, he or she could win all of that state's electoral votes. But if the former nominee won in a state that does have a law on how its electors vote, then one would have to look at that law's fine print to see what would happen and if the state's electoral votes could go to the replacement nominee.
Interesting. So in the examples you present, electors in Michigan and Colorado are required to vote for the candidate that appeared on the ballot. In Florida, the electors are required to vote for “the candidate of the party”, which could give leeway to vote for a replacement as long as that replacement becomes “the candidate of the party”.