"It's not like Pence automatically becomes the nominee," said Nathaniel Persily, a constitutional law expert at Stanford Law School. "Remember poor old Ted Cruz?"
Then comes the really hard part. Many states have already printed their ballots, and 400,000 early and absentee votes have already been cast, according to a tally by the United States Elections Project.
The party would have to persuade states to put the new nominee on the ballot by appealing to secretaries of state and seeking emergency injunctions through the courts - no easy lift at this late date.
"It seems very unlikely in most places that a court would order this, not only because ballots have been printed, but ballots have gone out to overseas and military voters," said Rick Hasen, a law professor and election law expert at the University of California at Irvine.
"While I think courts often will bend deadlines a little before there has actually been voting, now we're in a situation where that moment has passed."
Not to mention that there would be fierce legal pushback from Democrats.
"You will end up with lawyers on the other side saying, 'This is ridiculous, you can't allow them to game the system at this late stage,'" Persily said.
Still, some Republican election lawyers say the scenario is hypothetically possible.
"To be sure, it would be a gargantuan effort to try to replace Trump on state ballots across the country," said Robert Kelner, a veteran GOP lawyer who has represented party committees and presidential candidates. "But through appeals to secretaries of state and judicial relief, it can be done, up to a point. After that point, the party would have to depend on the judgment of members of the Electoral College."
That brings us to . . .
Option 2: Trump refuses to step down, and there is an unprecedented national effort to persuade state electors to vote for an alternative candidate.
The 538 members of the Electoral College are scheduled to gather on December 19 to cast their ballots for president and vice-president. That's usually just a formality.
But consider this scenario, posed by Edward Foley, director of election law at Moritz College of Law: What if Republicans abandon Trump and spend the next several weeks urging electors to vote for Pence or another alternative? It raises intriguing possibilities.
While many electors are bound by state law to vote for the candidate selected by the popular vote on November 8, there is precedent for "faithless" electors who have bucked that requirement. And it is unclear what legal remedies there would be to force them to comply, said Foley, author of Ballot Battles: The History of Disputed Elections in the United States.
"The Supreme Court has never settled the question of what happens if the electors vote on December 19 contrary to what the state vote assumes they will," he said. "What really matters is what gets sent to Congress on January 6."
And that's why, absent a clear victory by Democratic nominee Hillary Clinton, it could all come down to who controls Congress. If no candidate is able to reach the 270 majority in the electoral college on December 19, the decision on the next president would be decided by the House of Representatives in January.
If a Trump alternative somehow secured 270 votes and there was a dispute over whether that vote was valid, both chambers of Congress would have to decide whether to accept the electoral vote.
Veteran lawyers say it is highly improbable that the 2016 campaign will end up down this path.
"The state laws on electors are a real mishmash," said long-time Republican election-law attorney Ben Ginsberg. "And Trump had a big say in picking electors. You are asking the people who are loyal to him on a granular state level to do something other than support him. It's a real organisational triple bank shot."
Still, Foley noted that in the contentious presidential election of 1876 between Samuel Tilden and Rutherford Hayes, the votes of electors in four states were disputed, bringing the country to the brink of a constitutional crisis.
"My big takeaway away is that founders did not prepare us for this," Foley said. "We do not have the adequate constitutional infrastructure to handle this kind of scenario."
