How or why would any of these three states
secede?
Kentucky was majority Unionist, as shown in the 1861 state elections; so was Maryland, as was the majority of Missouri, despite Jackson's best efforts - less than 10 percent of Missouri's population were enslaved in the 1860 census, vis a vis about 20 percent of Kentucky's, while there were as many free blacks in Maryland as there wer slaves...and the Maryland legislature voted voted 53–13 against secession in 1861.
You may as well ask what the impact would be if Massachusetts, Michigan, and Maine had voted to secede.
Best,