“... it’s hard to see how it would have been abolished.”
The nation was already fighting politically over whether new states and territories would be slave or free. The issue was coming to a fight one way or the other.
The Republican Party was committed to a “free soil” position, not to allow slavery to spread. The Lincoln administration was open to a constitutional amendment protecting slavery where it already existed (although Lincoln was hopeful that it would eventually die out). The abolitionists were a small minority in the North. Poor whites in the North were probably no more enlightened in their racial views than poor whites in the South. States like Oregon forbade free persons of color from coming into the state. It wasn’t just the economics of slavery (which directly enriched only a small number of families) but racial attitudes, and perhaps fear of a Haiti-style massacre of whites if the slaves were suddenly set free.