No one can know for sure, but I am sure that the south would have rebelled no matter who was the Republican presidential nominee. They had threatened to rebel in 1856 if the republican nominee had won. I am also sure that pressure from the rest of America would not have allowed any of the other men to just let the south go. I think any President who did try and just let the south go would have been quickly impeached and removed from office. Hell, after Fort Sumter was fired on even spineless Buchanan supported force to put down the rebellion.
“the assault upon Sumter was the commencement of war by the Confederate states, and no alternative was left but to prosecute it with vigor on our part.” Birkner, Michael (September 20, 2005). “Buchanan’s Civil War”. Archived from the original on October 19, 2011. Retrieved December 22, 2013.
Many of the state’s legislatures issued resolutions strongly denouncing South Carolina’s secession. Here is the New York anti-secession resolution.
ANTI-SECESSION RESOLUTIONS OF THE NEW YORK LEGISLATURE
Passed by the New York State Assembly, 11 January 1861
[Text located by Sean Rogers, Furman University. Transcribed by Lloyd Benson from the New York Times, 12 January 1861]
Whereas, The insurgent State of South Carolina, after seizing the Post-offices, Custom-House, moneys and fortifications of the Federal Government, has, by firing into a vessel ordered by the Government to convey troops and provisions to Fort Sumter, virtually declared war; and
Whereas, The forts and property of the United States Government in Georgia, Alabama, and Louisiana have been unlawfully seized, with hostile intentions; and
Whereas, Their Senators in Congress avow and maintain their treasonable acts; therefore,
Resolved, (if the Senate concur,) That the Legislature of New York is profoundly impressed with the value of the Union, and determined to preserve it unimpaired; that it greets with joy the recent firm, dignified and patriotic Special Message of the President of the United States, and that we tender to him through the Chief Magistrate of our own State, whatever aid in men and money may be required to enable him to enforce the laws and uphold the authority of the Federal Government; and that, in the defence of the Union, which has conferred prosperity and happiness upon the American people, renewing the pledge given and redeemed by our fathers, we are ready to devote our fortunes, our lives, and our sacred honor.
Resolved, (if the Senate concur,) That the Union-loving citizens and representatives of Delaware, Maryland, Virginia, North Carolina, Kentucky, Missouri, and Tennessee, who labor with devoted courage and patriotism to withhold their States from the vortex of secession, are entitled to the gratitude and admiration of the whole people.
Resolved, (if the Senate concur,) That the Government be respectfully requested to forward, forthwith, copies of the foregoing resolutions to the President of the Nation, and the Governors of all the States of the Union.
And this resolution was passed prior to the firing on Fort Sumter. My opinion, and I know it’s only my opinion, war would have come no matter who was selected to be the Republican nominee for President.