Since the war was started by the insurrection, refusal to accept the insurrection was not the cause of the war. The people that started the war were in favor of the insurrection.
I get your point, but if the Union had rolled over and accepted the insurrection, there would have been no war.
Or rather, there would not have been a war then.
I fully believe that war would have arisen in a relatively short time over the border states, which the CSA wbeould have continued to try to subvert, or the territories, which they would have demanded be divided.