I guess this question applies more to the times leading to the war proper, but the idea is fundamentally the same: was it ever possible for secession to be an outcome? And if it was, who in the North advocated for it?
This comes up from time to time. u/Georgy_K_Zhukov posted a good answer to that here .
As for advocates, there were a few who at least talked of it being possible: notoriously, President Buchanan was very much a Southern sympathizer and seems to have had some idea of making it work, or was at least dithering over responding to it. And General "Fuss and Feathers" Winfield Scott was making noises about parting as friends. But they didn't try to work out a solution, propose how it could actually be done.
What seemed far more possible was getting the Southern states to rejoin by allowing them to continue to have slaves. There would be more than few Northerners who thought that would be a good idea, that the human cost of the war was not worth freeing the slaves. And after some years of Reconstruction after the War there would indeed be a general weariness of the North with the cost of military action in the South, which, combined with racism, led to abandonment of the idea of black liberation there.