What exactly to do with enslaved people who reached Union lines was an issue that came up early in the war. The most famous episode occurred shortly after the outbreak of hostilities at Fortress Monroe in Virginia when enslaved people presented themselves to the Union army. Enslaved people figured out very early what a war between the slave states and free could mean for them. The fort's commander, Benjamin Butler, improvised the famous doctrine of declaring the slaves of Confederates "contraband of war," and thus subject to forfeiture and seizure by the United States. Contraband camps of former slaves who left Confederate masters soon cropped up throughout areas under the jurisdiction of the US Army.

What the army was supposed to do with these people soon became a legal and administrative problem for Congress. At the beginning of the Civil War, slavery remained legal in the Union states - Maryland, Delaware, Kentucky, and Missouri were all still slave states in the beginning - and fighting a war of emancipation in the North remained a controversial idea in the North. Adopting as a matter of law the doctrine expounded by Butler was a convenient option, and Congress passed two Confiscation Acts creating the legal procedures to put it into effect, formalizing the forfeiture in law. By the time of the surrender of Vicksburg in July 1863, Congress had already passed the Act of Prohibiting the Return of Slaves in 1862, and there evidently some cases of enslaved people being returned to their masters early in the war. By the middle of the war, the Union had adopted as policy the weaponizing of slaves' legal status as slavery against the Confederacy.

It is important to realize, though, that the life of freed "contrabands" was not exactly easy. Though antislavery sentiment in the North was widespread, there was little enthusiasm for full racial equality. Many formerly enslaved people wound up performing manual labor for the US Army, or doing various kinds of support work in and around military installations. It should be noted as well that conditions in contraband camps were not always particularly good, and they were not necessarily a priority for the Army or for Congress. By 1863, though, there are formerly enslaved people wearing Union uniforms in organized regiments, such as the South Carolina Volunteer Infantry regiments composed of former slaves. There were, in fact, black units being organized for the Union army prior to the formation of the famous 54th Massachusetts.

In the situation you describe, we can't really say exactly what would happen, since we don't know all of the details and variables involved. It would be very likely, though, that you would wind up doing some kind of manual labor for the Union Army, and possibly enrolled in one of the black regiments once Congress authorized them.

Readings

James McPherson, Battle Cry of Freedom

Joseph Glatthaar, Forged in Battle: The Civil War Alliance of Black Soldiers and White Officers

Bruce Levine, The Fall of the House of Dixie

Bruce Levine, Confederate Emancipation: Southern Plans to Free and Arm Slaves During the Civil War

Eric Foner, Forever Free: The Story of Emancipation and Reconstruction

Amy Murrell Taylor, Journeys Through the Civil War's Slave Refugee Camps