Perhaps it was. Or, perhaps the thought was to ride it out until they could propose a Constitutional Amendment that would actually pass.
If there are any insights from the 1856 convention proceedings on how the Republicans figured to get three fourths of the several states to peaceably agree to an abolition amendment - I'd like to learn more about that business model. It would have solved a lot of problems.
In Lincoln's House Divided speech he predicted the end of slavery without specifying how. Since southern states knew Lincoln knew he could not get the super majority needed to peacefully overthrow constitutional slavery, they (southern states) figured he must have something else in mind.
Like confiscatory taxation which required a simple majority in Congress, not a super-majority.
Northern-financed murder raids could also be used to bring pressure.
Refusal to honor the provisions of the constitution which benefited the South could be used to bring pressure.
And, if control of the U.S. military could be obtained by the election of a regional candidate with as little as 39 percent of the vote, then northern options would not be necessarily limited to the peaceful overthrow of constitutional slavery.