"IF" it didn't cross their minds they had to be seriously ignorant. What you are asking was exactly what the southern plantation owners and politicians were asking for. The British had already used the same plan to enamcipate their slaves by the 1830's. The re-colonization program was in full stride in Washington D.C. 3,000 slaves were expatriotated to Liberia and Monroevia during the war at a cost of $3,000,000 the cost of one day of the war. And Abraham Lincoln's own Father-in-law, Mary Todd's own father, was an ex-slave owner who was very much supportive of the re-colonization program.