Let's say Lincoln Virginian secession is avoided by Lincoln somehow and the knock-on effect is that Tennessee and North Carolina remain in the Union as well. Arkansas still secedes due to being a cotton state.
The Confederate States violate the neutrality of the Upper South as they did in Kentucky historically. The Union is thus united against the Confederacy.
With no Virginian Secession, the confederacy is deprived of the Tredegar Iron Works and the Norfolk Naval Yard. Tredegar was the only major foundry in the whole Confederacy and Norfolk's naval guns were used to defend the Confederate Coast from Virginia to Louisiana and were used to defend the Mississippi. Plus Virginia was an important source of Copper and Salt, important war materials. Throw on top of this the massive manpower deficiency, and the Confederacy is cooked by 1862-1863.
The emancipation proclamation, which didn't apply to Union States historically, still occurs.
What is reconstruction of the 8 Confederate States like? With less territory to occupy, could it be more thorough and successful?
Could we see a State of Nickajack carved out of unionist North Alabama?
If you avoid "Redeemer" governments in the deep south, there's likely an abolitionist majority in the Senate, no?