The longer the CSA is independent, the more likely this is to be the case. The only analogy I can think of is the collapse of the Russian Empire, and the Reconquest of that Empire by the Communist Afterwards. If loosing the the ACW caused a radical party to come to power withing 10 years, I could see a ideoilogical based reconquest of the CSA. But traditional American politics won't lead to it, you'd need some revolutionary bent to it. (But Politics as we know it ends if the CSA wins, especially if they don't win by 1862, so whatever.)
Although most people assume the Post-Lost USA would be pretty conservative, and I'm not so sure of that, depending on how and when the loss occured. We're used to Northerners having no identity, but I iimagine there is at least a 50% chance that some "wierd" by our standards northern identity could take hold among the vetrans, first, who refused to believe all their friends died in vain, nor their lifelong cripplings.
What is the North going to say to 2,000,000 vetrans and another million orphans and widows? "My bad? Nevermind? Forget About It."
I don't think it will be that way mainly because 1. The Confederate States are united by the fact they hate the United States ("Yankee agressors" as they would call them) and fought a war to secede from the North so there's no way any of the 13 southern states (Arkansas, Arizona, Alabama, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, Sequoyah/Oklahoma/whatever it's called, Tennessee, Texas, and Virginia) will ever try to rejoin the USA no matter how bad the situation may be and 2. The U.S. already would be hostile and so would it's citizens towards the newly-independent CSA. I do agree Byron that that it would be almost impossible for a ideological conquest of the CSA by the USA under traditional American politics.
Also, furthering on a post Post-Lost USA I would say it would become more liberal and progressive in terms of Negro rights and slavery since the nation's most conservative region the South/CSA has already seceded though there would still be some nativist and anti-immigrant elements that exist (anti-Irish, anti-Chinese, anti-Italian, etc.). For my case that there would be an American revanchism (a la French irridentism), the whole thing about 2 million veterans and another million orphans and widows it's so massive I can't imagine the North/USA ever trying to forget about them they would already have been reminded that they were in a massive war that saws hundreds of thousands die and was costly plus these veterans, orphans, and widows would see the now independent Southern states as "lost territory" (since the likes of Virginia, North Carolina, South Carolina, and Georgia all fought for the Union during the American Revolutionary War, Tenneessee being a part of the U.S. since 1796, the Louisiana Purchase, Texas willingly joined the Union in 1845, and the Arizona and Seqouyah southern states once being U.S. territories) under an "illegal" government (the CSA) and that those states should be taken back, they would begin to spread these ideas in Northern newspapers and when they reach the masses they will soon believe them.
As for any Northern/American identity, there was already one dating back to the Revolutionary War prior to the Civil War and a new rival in the form of the CSA would mean the USA would try to reform that image to fit with their conflict with the Confederacy.