Remember that under the Constitution as it exists today, states are granted a good deal of leeway as to how they assign -- or in this case, RE-assign -- their electoral votes.
Let's suppose that ol' white joe DOES abandon his re-election quest, and another candidate is nominated (or more correctly, "assigned") by the dem/communist convention in Chicago.
And let's also suppose that under the existing laws of a few states, there is no legal action taken to remove ol' joe from the ballot, and enter his "replacement".
Just let it all go like that until election day.
If it's a red state, the vote is probably going to the electors for Mr. Trump in any case. The "electors" for ol' joe won't matter. They'll be forgotten.
If it's a blue state, the voters WILL vote for ol' joe's electors. Let them.
At this point, post-election, the state legislatures will now have to handle the hot potato of WHAT TO DO with those electors.
They could do nothing -- i.e., ignore the reality that their electors have been chosen for a non-existent candidate -- and thus receive no representation within The Electoral College when it convenes. They're not going to permit that.
OR...
They can instruct those electors to cast their votes for the actual dem/com replacement candidate at the Electoral College. I seriously doubt that ANY elector who was originally chosen to represent ol' joe would not be willing to vote for his replacement instead.
I'll go so far as to say that any elector who refused to do so might be replaced by the state involved. Remember, the Constitution gives the states the right to determine how electors will be chosen.
If there are objections, this may well be adjudicated in emergency session by the U.S. Supreme Court.
This hoopla about "no replacement candidate on the ballot" is a smokescreen, a Hitchcock-style McGuffin to keep you confused and disoriented.
Nothing more.
